Polymer dispersed liquid crystal display device, and a method for producing the same, wherein the polymer forms walls

ABSTRACT

A liquid crystal display device according to the present invention includes a pair of electrode substrates and a polymer dispersed liquid crystal complex film interposed between the pair of substrates. The polymer dispersed liquid crystal complex film includes a liquid crystal composition and a polymer resin composition. It is ensured that a value ΔT is 25° C. or less, and a glass transition temperature T g  of the polymer resin composition is 60° C. or more, the value ΔT being defined as a difference between a phase transition temperature T CI  of the liquid crystal composition between a liquid crystal phase and an isotropic liquid phase thereof and a phase transition temperature T matrix  of the polymer dispersed liquid crystal complex film.

This is a division of U.S. Ser. No. 08/128,300, filed Sep. 29, 1993, nowU.S. Pat. No. 5,450,220.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polymer dispersed liquid crystalcomplex film, a liquid crystal display device, and a method forproducing the same. A polymer dispersed liquid crystal display deviceaccording to the present invention is, owing to a broad range of viewingangles thereof, applicable to a flat display device such as a liquidcrystal panel to be used in an optical projector, a personal computer,an amusement device, or a television set. Moreover, the polymerdispersed liquid crystal display device is, owing to the excellentlyuniform contrast thereof, applicable to a display device to be used in aprojection display. Furthermore, the polymer dispersed liquid crystaldisplay device is, in view of a shutter effect thereof, applicable to adisplay board, a window, a door, a wall, and the like.

2. Description of the Related Art

There have been realized display devices of a TN (Twisted Nematic) modeor an STN (Super Twisted Nematic) mode, as display devices utilizingelectrooptical effects. Both display modes use nematic liquid crystal. Adisplay mode using ferroelectric liquid crystal has also been proposed.However, these display modes require a polarizing plate and anorientation treatment. Display modes which utilize the light-scatteringproperty of liquid crystal but do not require a polarizing plate are,for example, a DS (Dynamic Scattering) mode and a PC (Phase Change)mode.

There has been developed a display device which requires neither apolarizing plate nor an orientation treatment. It is known that such adisplay device can be realized by dispersing liquid crystal dropletssealed in capsules in a polymer medium so as to form a film. Proposedmaterials for forming such capsules are gelatine, gum arabic,polyvinylalcohol, and the like, as is disclosed in Japanese NationalPublication No. 58-501631, U.S. Pat. No. 4,435,047, etc.

This type of conventional art amounts to the following technique: Anordinary refractive index n_(o) of a liquid crystal molecule and arefractive index n_(p) of the polymer medium are made to be equal. As aresult, a transparent state is displayed when a voltage is applied,since the liquid crystal molecules are oriented in the same direction. Awhite state is displayed when no voltage is applied, since the liquidcrystal molecules are oriented in various directions (randomorientation) so that the refractive indices of the liquid crystaldroplets deviate from the ordinary refractive index n_(o), causingscattering of light at interfaces of the liquid crystal and the polymer.Inevitably, it is necessary to carefully choose a liquid crystalmaterial and a polymer material in order to ensure that the ordinaryrefractive index n_(o) of the liquid crystal and the refractive indexn_(p) of the polymer are approximately the same so that light issufficiently transmitted when a voltage is applied. Japanese Laid-OpenPatent Publication Nos. 63-43993 and 3-245120 disclose methods forproducing a transparent liquid crystal panel by ensuring that the ratioof the ordinary refractive index n_(o) of liquid crystal to therefractive index n_(p) of a polymer film are in the range of 0.98 to1.02.

A polymer dispersed liquid crystal display device has also been proposedwhich utilizes the same principle as that described above. This displaydevice is a liquid crystal display device using a polymer dispersedliquid crystal complex film. The complex film has a structure in whichliquid crystal regions, each constituted essentially by a liquid crystaldroplet or continuous liquid crystal droplets, are partitioned bypolymer walls. A known method for producing such a polymer dispersedliquid crystal display device is disclosed in Japanese NationalPublication No. 61-502128. In this method, in order to attain sufficientcontrol of the diameters of liquid crystal droplets, the above-mentionedliquid crystal display device is produced through phase separation,starting from a mixture of a liquid crystal material and a light-curable(photopolymerizable) material.

Some conventional modes In which scattering of light occurring atinterfaces of liquid crystal regions and polymer walls is controlled areapplicable to a polymer dispersed liquid crystal device. Examples ofsuch conventional modes are a TN mode, an STN mode, an ECB (electricallycontrolled birefringence) mode, and an FLC (Ferroelectric LiquidCrystal) mode.

In a case where a polymer dispersed liquid crystal device is used as aliquid crystal device for optical projection, or as a transmissionliquid crystal display device provided with a back light, displaycharacteristics of the liquid crystal device are required to be stableagainst heat for long periods so as to cope with heating effects due toemission of light by a metal halide lamp used as a light source, acold-cathode tube, an EL film, and the like, and/or emission of heat inthe operation of the device.

However, a liquid crystal display device produced with the above methodhas the following problems: a) a display panel of the liquid crystaldisplay device has poor resistance against heat because of a mutualdissolution effect of the liquid crystal material and the polymer(light-curable) material, that is, dissolution of unreactedlight-curable monomers and oligomers into the liquid crystal materialand elution of the liquid crystal material into the polymer material; b)display characteristics of the liquid crystal panel are influenced bychanges in thermal circumstances; c) the response speed of the liquidcrystal decreases because the viscosity of the liquid crystal materialincreases owing to the above-mentioned mutual dissolution effect.

Japanese Laid-Open Patent Publication Nos. 3-219211, 4-1724, 4-70714,etc. are known to deal with improvement of heat resistance of liquidcrystal display devices, describing a glass transition temperature T_(g)of a polymer material to be used for a matrix. However, in consideringthermal characteristics of a whole panel of a polymer dispersed liquidcrystal device or a polymer-matrix type liquid crystal device, influenceof the liquid crystal material, which is a main component of the device,must be taken into account. In particular, thermal characteristics of acomplex system consisting of materials of different kinds, such as aliquid crystal-polymer complex film, are known to be different fromthose of a single material film. Therefore, it is insufficient to payattention only To the glass transition temperature T_(g) of the polymermaterial to consider heat resistance that affects the displaycharacteristics. Moreover, any of the methods for producing a polymerdispersed liquid crystal device disclosed in the above publications is a`solvent evaporation method`, in which the liquid crystal material andthe polymer material are dissolved in a common solvent, applied to asubstrate, and then dried so as to form a thin film containing liquidcrystal. Since it is difficult to control a phase separation process ofa mixture of the liquid crystal material and the polymer material bythis solvent evaporation method, a polymer dispersed liquid crystaldevice produced thereby inevitably has a very high driving voltage. As aresult, such a polymer dispersed liquid crystal, when applied to a flatpanel display of an active matrix driving system, has a problem that theflat panel display is difficult to be realized since the driving voltagetherefor exceeds the withstand voltage of an LSI circuit used in adriving circuit.

Effects of a glass transition temperature T_(g) of a polymer material onelectrooptical characteristics of polymer dispersed liquid crystal arealso described in "Appl. Phys. Lett. 60, 3238 (1992)". However, a liquidcrystal device disclosed in this article is also produced by a solventevaporation method, and therefore has a major problem that its drivingvoltage exceeds 50 V.

Moreover, "Extended Abstracts", p. 310 (The 17th Liquid Crystal Forum,1991) reports on a relationship between voltages and lighttransmittances, and on methods to realize a higher response speed, withrespect to a polymer dispersed liquid crystal display device in whichsmall amounts of cholesteric liquid crystal and smectic liquid crystalare added. However, the liquid crystal display device reported in theabove has such display quality problems that contrast thereof is lowbecause of insufficient light-scattering characteristics, and that thevoltage-transmittance hysteresis is large, and that it is difficult torealize intermediate gray tones.

On the other hand, Japanese Laid-Open Patent Publication No. 4-14015discloses a material including a polymer containing fluorine, as a resinmaterial for forming a polymer wall. However, no attention is paid toinfluences of thermal circumstances on display characteristics,including heat resistance, of a liquid crystal panel in the structure.The structure therefore has poor practicality.

A conventional liquid crystal display mode which utilizes opticalrotatory power of liquid crystal molecules is known to have a majorproblem of insufficient viewing angle characteristics. This problem willbe described with reference to FIGS. 16A to 16C, which arecross-sectional views showing a conventional liquid crystal displaydevice of a TN mode. As is shown in FIGS. 16A to 16C, this liquidcrystal display device of a TN mode has a structure in which a displaymedium including liquid crystal molecules 11 are interposed between apair of substrates 12 and 13. FIG. 16A describes an initial state of theliquid crystal display device; FIG. 16B describes a state where theliquid crystal display device is displaying an intermediate gray tone;FIG. 16C describes a state where the liquid crystal device is beingtransparent.

In an initial state, as is shown in FIG. 16A, the liquid crystalmolecules 11 are twisted by 90°, and also stand at a certain angle(pre-tilt angle) in one direction. In a transparent state, as is shownin FIG. 16C, the liquid crystal molecules 11 are oriented verticallywith respect to the substrates 12 and 13. Therefore, each liquid crystalmolecule 11 stands at the same angle, irrespective of the viewing angle.In other words, each liquid crystal molecule 11 has the same apparentrefractive index irrespective of the viewing angle. However, in a statewhere the liquid crystal display device is displaying an intermediategray tone, as is shown in FIG. 16B, since the liquid crystal molecules11 are oriented at certain angles with respect to the normal line of thetransparent substrates 12 and 13, the liquid crystal molecules 11, asobserved from a direction A, stand at different angles than in caseswhere they are observed from a direction B. In other words, the apparentrefractive index of each liquid crystal molecule 11 varies depending onthe viewing angle. As a result, contrast of an image displayed on thedisplay device greatly varies depending on whether the image is observedfrom the direction A or the direction B. In some extreme cases, displaydefects such as inversion of the image occur. As is described above,conventional display modes have a problem of inadequate viewing anglecharacteristics.

The inventors previously invented a polymermatrix type liquid crystaldisplay device in which a liquid crystal material is gathered in pixelregions of a liquid crystal panel, and liquid crystal domains aredisposed radially in each pixel region. The liquid crystal displaydevice is bright, and has drastically improved viewing anglecharacteristics. The liquid crystal display device, in reference to thestructure thereof, includes a pair of substrates, polymer walls (whichconsist essentially of a polymer material) arranged in a matrix shapeinterposed between the substrates, liquid crystal regions partitioned bythe polymer walls, and at least one polarizing plate formed on thesubstrates. Within each liquid crystal region, liquid crystal moleculesgradually stand in the directions of the polymer walls as a voltage isapplied, owing to an interaction of the liquid crystal molecules and thepolymer walls. Therefore, as is described above, the apparent refractiveindex of the liquid crystal molecules as a whole becomes substantiallythe same irrespective of the viewing angle, whereby the viewing anglecharacteristics are greatly improved.

The polymer matrix type liquid crystal display device uses a mixtureconsisting of materials similar to those which were disclosed in theabove-mentioned Japanese National Publication No. 61-502128, and isproduced by irradiating the mixture with light, while disposing alight-intercepting object such as a photomask over the pixel regions.Accordingly, this liquid crystal display device, invented by theinventors, has the same problems as those of the conventional polymerdispersed liquid crystal display device disclosed in Japanese NationalPublication No. 61-502128.

Moreover, in the above-mentioned liquid crystal display device, liquidcrystal domains of each liquid crystal region are oriented eitherradially or randomly with respect to the center of the correspondingpixel. Therefore, scattering of light occurs locally at interfaces ofthe liquid crystal and the polymer walls in cases where the liquidcrystal and the polymer walls have a large difference in refractiveindices thereof. Accordingly, there has also been a problem of lowdisplay quality, etc. because the contrast of the display device is lowand a displayed image has a coarse appearance.

SUMMARY OF THE INVENTION

A polymer dispersed liquid crystal complex film according to the presentinvention comprises: a liquid crystal composition; and a polymer resincomposition, wherein a value ΔT is 25° C. or less and a glass transitiontemperature T_(g) of the polymer resin composition is 60° C. or more,the value ΔT being defined as a difference between a phase transitiontemperature T_(matrix) of the polymer dispersed liquid crystal complexfilm and a phase transition temperature T_(CI) of the liquid crystalcomposition between a liquid crystal phase and an isotropic liquid phasethereof.

Alternatively, a liquid crystal display device according to the presentinvention comprises: a pair of electrode substrates; and a polymerdispersed liquid crystal complex film interposed between the pair ofsubstrates, the polymer dispersed liquid crystal complex film includinga liquid crystal composition and a polymer resin composition, wherein avalue ΔT is 25° C. or less, and a glass transition temperature T_(g) ofthe polymer resin composition is 60° C. or more, the value ΔT beingdefined as a difference between a phase transition temperature T_(CI) ofthe liquid crystal composition between a liquid crystal phase and anisotropic liquid phase thereof and a phase transition temperatureT_(matrix) of the polymer dispersed liquid crystal complex film.

In one embodiment of the invention, the value ΔT is 10° C. or less.

In another embodiment of the invention, the liquid crystal compositionhas a positive anisotropy of dielectric constant, and includes at leastone of a fluorine-compound and a chlorine-compound.

In still another embodiment of the invention, the polymer resincomposition includes at least one selected from the group consisting ofa fluorine-containing polymer, a chlorine-containing polymer, and asilicon-containing polymer.

In still another embodiment of the invention, the liquid crystalcomposition includes at least one dichroic dye.

In still another embodiment of the invention, the liquid crystalcomposition includes at least one of an optically active chiral dopantand a cholesteric liquid crystal added in a ratio, by weight, in therange of 0.1% to 10% thereto.

In still another embodiment of the invention, orientation means fororienting the liquid crystal composition is provided for at least one ofthe substrates.

In still another embodiment of the invention, the orientation meansincludes an insulating film.

Alternatively, a liquid crystal display device according to the presentinvention comprises: a pair of electrode substrates; and a displaymedium interposed between the pair of substrates, the display mediumincluding a polymer matrix and at least one liquid crystal regionpartitioned by the polymer matrix, the polymer matrix being made of apolymer resin composition, and the liquid crystal region being made of aliquid crystal composition, wherein a value ΔT is 25° C. or less, and aglass transition temperature T_(g) of the polymer resin composition is50° C. or more, the value ΔT being defined as a difference between aphase transition temperature T_(matrix) of the display medium and aphase transition temperature T_(CI) of the liquid crystal compositionbetween a liquid crystal phase and an isotropic liquid phase thereof.

In one embodiment of the invention, the value ΔT is 10° C. or less.

In another embodiment of the invention, each liquid crystal region has asurface parallel to each of the pair of electrode substrates, andoccupies a larger area inside a pixel region than outside the pixelregion.

In still another embodiment of the invention, the liquid crystalcomposition has a positive anisotropy of dielectric constant, andincludes at least one of a fluorine-containing compound and achlorine-containing compound.

In still another embodiment of the invention, the polymer resincomposition includes at least one selected from the group consisting ofa fluorine-containing polymer, a chlorine-containing polymer, and asilicon-containing polymer.

In still another embodiment of the invention, the liquid crystalcomposition includes at least one dichroic dye.

In still another embodiment of the invention, the liquid crystalcomposition includes at least one of an optically active chiral dopantand a cholesteric liquid crystal added in a ratio, by weight, in therange of 0.1% to 10% thereto.

In still another embodiment of the invention, orientation means fororienting the liquid crystal composition is provided for at least one ofthe substrates.

In still another embodiment of the invention, the orientation meansincludes an insulating film.

In still another embodiment of the invention, a polarizing plate isprovided on at least one of the substrates.

A method for producing a polymer dispersed liquid crystal complex filmaccording to the present invention includes the steps of: a step forpreparing a mixture of a polymerizable material and a liquid crystalmaterial, wherein the polymerizable material includes a monofunctionalmonomer and at least one of a multifunctional monomer and amultifunctional oligomer mixed at a ratio in the range of 93:7 to 40:60;and a phase separation step for processing the mixture into a polymerdispersed liquid crystal complex film by a phase separation conductedthrough polymerization, the polymer dispersed liquid crystal complexfilm consisting of a liquid crystal composition and a polymer resincomposition, wherein a value ΔT is 25° C. or less, and a glasstransition temperature T_(g) of the polymer resin composition is 60° C.or more, the value ΔT being defined as a difference between a phasetransition temperature T_(matrix) of the polymer dispersed liquidcrystal complex film and a phase transition temperature T_(CI) of theliquid crystal composition between a liquid crystal phase and anisotropic liquid phase thereof.

Alternatively, a method for producing a polymer dispersed liquid crystaldisplay device according to the present invention includes the steps of:a step for preparing a mixture of a polymerizable material and a liquidcrystal material, wherein the polymerizable material includes amonofunctional monomer and at least one of a multifunctional monomer anda multifunctional oligomer mixed at a ratio in the range of 93:7 to40:60; and a phase separation step for processing the mixture by a phaseseparation conducted through polymerization into a polymer dispersedliquid crystal complex film as a display medium interposed between apair of electrode substrates, the polymer dispersed liquid crystalcomplex film consisting of a liquid crystal composition and a polymerresin composition, wherein a value ΔT is 25° C. or less, and a glasstransition temperature T_(g) of the polymer resin composition is 60° C.or more, the value ΔT being defined as a difference between a phasetransition temperature T_(matrix) of the polymer dispersed liquidcrystal complex film and a phase transition temperature T_(CI) of theliquid crystal composition between a liquid crystal phase and anisotropic liquid phase thereof.

In one embodiment of the invention, the phase separation step includes afirst phase separation step for phase-separating the mixture throughpolymerization, and a second phase separation step for furtherphase-separating the mixture through polymerization, the second phaseseparation step being conducted at a lower temperature than the firstphase separation step.

In another embodiment of the invention, the polymerization is conductedby irradiating the mixture with light, the light having a distributionof intensities ranging from high to low.

In still another embodiment of the invention, the light having adistribution of intensities ranging from high to low is obtained throughmeans for substantially lowering the intensity of the light at a pixelregion.

In still another embodiment of the invention, the liquid crystalcomposition obtained through the phase separation step has a positiveanisotropy of dielectric constant, and includes at least one of afluorine-containing liquid crystal compound and a chlorine-containingliquid crystal compound.

In still another embodiment of the invention, the polymer resincomposition obtained through the phase separation step includes at leastone selected from the group consisting of a fluorine-containingcompound, a chlorine-containing compound, and a silicon-containingcompound.

In still another embodiment of the invention, the liquid crystalcomposition obtained through the phase separation step includes at leastone dichroic dye.

In still another embodiment of the invention, the liquid crystalcomposition obtained through the phase separation step includes at leastone of an optically active chiral dopant and a cholesteric liquidcrystal added in a ratio, by weight, in a range of 0.1% to 10% thereto.

Alternatively, a liquid crystal display device according to the presentinvention comprises: a pair of electrode substrates; and a displaymedium interposed between the pair of substrates, the display mediumincluding a polymer matrix and at least one liquid crystal regionpartitioned by the polymer matrix, the polymer matrix being made of apolymer resin composition, and the liquid crystal region being made of aliquid crystal composition, wherein a refractive index n_(p) of thepolymer resin composition, an ordinary refractive index n_(o) of theliquid crystal composition, and an extraordinary refractive index n_(e)of the liquid crystal composition satisfy the following relationship:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2.

In one embodiment of the invention, each liquid crystal region includesat least one liquid crystal domain oriented randomly.

In another embodiment of the invention, each liquid crystal regionincludes at least one liquid crystal domain oriented radially.

In still another embodiment of the invention, orientation means fororienting the liquid crystal composition is provided for at least one ofthe substrates.

In still another embodiment of the invention, a polarizing plate isprovided on at least one of the substrates.

Alternatively, a method for producing a liquid crystal display deviceincludes the steps of: a step for preparing a mixture of a polymerizablematerial and a liquid crystal material; and a phase separation step forforming a display medium made of a polymer resin composition and aliquid crystal composition by phase separation through polymerizationconducted by irradiating the mixture with light having a distribution ofintensities ranging from high to low, the display medium interposedbetween a pair of substrates, wherein a refractive index n_(p) of thepolymer resin composition, an ordinary refractive index n_(o) of theliquid crystal composition, and an extraordinary refractive index n_(e)of the liquid crystal composition satisfy the following relationship:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2.

In one embodiment of the: invention, the light having a distribution ofintensities ranging from high to low is obtained through means forsubstantially lowering the intensity of the light at a pixel region.

A polymer dispersed liquid crystal complex film and a liquid crystaldisplay device according to the present invention includes a liquidcrystal composition and a polymer resin composition. The polymerdispersed liquid crystal display device and the liquid crystal displaydevice each have a value ΔT of 25° C. or less, and a glass transitiontemperature T_(g) of 60° C. or more. The value ΔT is correlated withelectrooptical characteristics and heat resistance characteristics, sothat the electrooptical characteristics and the thermal characteristicsare improved by ensuring that the value ΔT is 25° C. or more.

In a method for producing a polymer dispersed liquid crystal complexfilm and a liquid crystal display device according to the presentinvention, phase separation of the liquid crystal composition and thepolymer resin composition is conducted through two polymerizationreactions. Phase separation through a polymerization reaction isconducted at a lower temperature at the second phase separation stepthan at the first phase separation step. Thus, although an amount of apolymerizable material remains unreacted, i.e. unpolymerized, andtherefore is dissolved in the liquid crystal composition at the firstphase separation step, a portion of the polymerizable material comes outundissolved so as to be polymerized at the second phase separation step,thus further advancing the phase separation. Accordingly, the amount ofthe unreacted polymer material which is dissolved in the liquid crystalcomposition is reduced. In other words, the value ΔT can be furtherreduced by the method according to the present invention.

Moreover, in a method for producing a polymer dispersed liquid crystalcomplex film and a liquid crystal display device according to thepresent invention, the polymerization reaction is conducted byirradiating a mixture of a liquid crystal material and a polymerizablematerial with light having intensities ranging from high to low. Thelight is obtained by the use of a photomask or the like. Herein, apolymer matrix is formed in a portion of the mixture that is irradiatedwith light having a high intensity (hereinafter referred to as"strongly-irradiated region"), while a liquid crystal region is formedin a portion of the mixture that is irradiated with light having a lowintensity (hereinafter referred to as "weakly-irradiated region").Viewing angle characteristics can be improved by ensuring that theliquid crystal regions correspond to pixel regions.

Moreover, a polymer-matrix type liquid crystal display device accordingto the present invention uses a mixture of a liquid crystal material anda polymerizable material that are so prescribed as follows: A refractiveindex n_(p) of a resultant polymer obtained through polymerization, andan ordinary refractive index n_(o) and an extraordinary refractive indexn_(e) of the liquid crystal have the following relationship:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2

As a result, scattering of light is restrained from occurring atinterfaces of liquid crystal regions and a polymer matrix of thepolymer-matrix type liquid crystal display device.

Thus, the invention described herein makes possible the advantages of(1) providing a liquid crystal device and a method for productionthereof, the liquid crystal device having improved heat resistance so asto have a smaller influence on display characteristics of the liquidcrystal device, and to have a low driving voltage and excellent displaycharacteristics such as contrast characteristics, voltage-trans mittancehysteresis characteristics, voltage-holding ratio characteristics, andviewing characteristics; and (2) providing a liquid crystal displaydevice having high display quality in which a displayed image does nothave a coarseness problem, and a method for production thereof.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for describing a difference ΔT betweenphase-transition endothermic peaks of a liquid crystal material and apolymer dispersed liquid crystal complex film.

FIG. 2 is a schematic diagram for describing a glass transitiontemperature T_(g) of a polymer resin composition.

FIG. 3A is a cross-sectional view of a liquid crystal display deviceaccording to the present invention in a state where an intermediate graytone is displayed, and it describes improvement of viewing anglecharacteristics of the device.

FIG. 3B is a cross-sectional view of a liquid crystal display deviceaccording to the present invention when being transparent, and itdescribes improvement of viewing angle characteristics of the device.

FIG. 4A is a schematic cross-sectional view of a liquid crystal displaydevice when produced by a method according to the present invention, andit shows a state before the device is irradiated with light.

FIG. 4B is a schematic cross-sectional view of a liquid crystal displaydevice when produced by a method according to the present invention, andit shows a state after the device is irradiated with light.

FIGS. 5A and 5B are views showing patterns of a photomask used inproduction of a liquid crystal display device according to the presentinvention.

FIG. 6 is a schematic plane view showing one embodiment of a liquidcrystal display device according to the present invention.

FIG. 7 is a schematic cross-sectional view showing one embodiment of aliquid crystal display device according to the present invention.

FIG. 8 is a circuit diagram of an apparatus for measuring avoltage-holding ratio.

FIG. 9 is a view showing a pattern of a pattern for a photomask used inproduction of a liquid crystal display device according to Example 14 ofthe present invention.

FIG. 10 is a plane view showing a pixel region of a liquid crystaldisplay device according to Example 14 of the present invention.

FIG. 11 is a set of graphs (a) to (e), showing the dependence ofelectrooptical characteristics of a liquid crystal display deviceaccording to Example 14 of the present invention on viewing angles.

FIG. 12 is a diagram for describing the viewing angle in each of graphs(a) to (e) of FIG. 11.

FIG. 13A is a cross-sectional view of a liquid crystal cell of a TN typeaccording to Example 18 of the present invention in an initial state.

FIG. 13B is a cross-sectional view of a liquid crystal cell of a TN typeaccording to Example 18 in a state where an intermediate gray tone isdisplayed.

FIG. 13C is a cross-sectional view of a liquid crystal cell of a TN typeaccording to Example 18 in a transparent state.

FIG. 14 is a plane view showing pixel regions of a liquid crystaldisplay cell shown in FIGS. 13A to 13C.

FIG. 15 is a diagram for describing a range of refractive indices inExample 18.

FIG. 16A is a cross-sectional view of a conventional liquid crystaldisplay device of a TN type in an initial state, and it describesimprovement of the viewing angle characteristics of the device.

FIG. 16B is a cross-sectional view of a conventional liquid crystaldisplay device of a TN type in a state where an intermediate gray toneis displayed, and it describes improvement of the viewing anglecharacteristics of the device.

FIG. 16C is a cross-sectional view of a conventional liquid crystaldisplay device of a TN type when transparent, and it describesimprovement of the viewing angle characteristics of the device.

FIG. 17 is a graph showing the relationship between a transmittanceT_(ON) of a liquid crystal cell when a voltage is applied thereto andthe absolute value of a difference between an ordinary refractive indexn_(o) of liquid crystal and a refractive index n_(p) of a polymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present application adopts the following terminology.

A phase transition temperature T_(CI) means a transition temperaturebetween a liquid crystal phase and an isotropic liquid phase of a liquidcrystal composition in a bulk state, namely a pure liquid crystalcomposition. A liquid crystal composition means a composition includedin a polymer dispersed liquid crystal complex film and a polymer-matrixtype liquid crystal display device, and consists essentially of a liquidcrystal compound. Strictly speaking, a liquid crystal composition meansa system which consists mainly of a plurality of liquid crystalcompounds and includes a small amount of a chiral dopant and, ifnecessary, a coloring substance. A phase transition temperatureT_(matrix) means a phase transition temperature of a polymer dispersedliquid crystal complex film obtained by subjecting a mixture of apolymerizable material and a liquid crystal material to a phaseseparation process conducted through a polymerization reaction. Thephase transition temperatures T_(CI) and T_(matrix) correspond totemperatures (°C.) at which an endothermic characteristic curve has apeak, as is shown in FIG. 1. An endothermic degree at a giventemperature is measured by a DSC (Differential Scanning Calorimetry)method. The endothermic peak of the complex film arises due to softeningand/or glass transition of a liquid crystal composition and a polymerresin composition within the complex film. A polymer resin compositionmeans a composition included in the polymer dispersed liquid crystalcomplex film and the polymer-matrix type liquid crystal display device,and is a composition mainly containing a polymer (resin) compound,obtained through the phase separation. A value ΔT is defined as anabsolute value of a difference between the phase transition temperatureT_(CI) between a liquid crystal phase and an isotropic liquid phase andthe phase transition temperature T_(matrix) of the complex film.

A glass transition temperature T_(g) means a glass transitiontemperature for the polymer resin composition. A glass transitiontemperature is a value inherent to a given material, and can beevaluated by a DSC method, a viscoelasticity measurement, or the like.In the case of the polymer resin composition according to the presentinvention, the glass transition temperature T_(g) thereof is obtained inthe following manner: the polymer resin composition, which remains afterremoving the liquid crystal composition from the polymer dispersedliquid crystal complex film or the polymer-matrix type liquid crystaldisplay device is subjected to a DSC method so as to obtain acharacteristic curve of DSC values; the glass transition temperatureT_(g) is defined as a temperature (°C.) at an intersection of asymptoticlines A and B of the curve of DSC values, as is shown in FIG. 2.

The polymer dispersed liquid crystal complex film of the presentinvention includes the liquid crystal composition and the polymer resincomposition. The liquid crystal composition forms droplets of liquidcrystal in the polymer resin composition. The complex film has a valueΔT of 25° C. or less and a glass transition temperature T_(g) of 60° C.or more.

As is described above, in the polymer dispersed liquid crystal complexfilm of the present invention, thermal characteristics of its componentsare ensured to fall within a certain range. By doing so, heat resistancecharacteristics of a liquid crystal panel of a liquid crystal device canbe improved.

Firstly, the value ΔT should be 25° C. or less, and preferably be 10° C.or less. When the value ΔT is 10° C. or less, a liquid crystal deviceusing this complex film has a sufficiently high response speed in termsof the practicality thereof. It is recognized that an increased amountof the polymer resin composition and the like are mixed within dropletsof liquid crystal in the polymer dispersed liquid crystal complex filmas the value ΔT increases. On the other hand, the liquid crystaldroplets are more likely to reflect original properties of the liquidcrystal composition as the value ΔT decreases.

The value ΔT has to do with electrooptical effects of the polymerdispersed liquid crystal complex film, especially the response speed andvoltage-transmittance hysteresis characteristics. Moreover, the value ΔTis important when considering influences of heat resistancecharacteristics on the electrooptical effects such as the response speedand voltage-transmittance hysteresis characteristics of the polymerdispersed liquid crystal complex film.

"Polymer Preprints, Japan, vol. 38, No. 7, 2154 (1989)" discloses anexample of a system whose value ΔT is small. However, this article doesnot mention influences of heat resistance characteristics on displaycharacteristics at all.

Secondly, the glass transition temperature T_(g) should be 60° C. ormore, and preferably be 80° to 180° C. The inventors found the followingcorrelation between the value ΔT and the glass transition temperatureT_(g) of a polymer dispersed liquid crystal complex film: a polymerwhich has a high glass transition temperature T_(g) and therefore tendsto form a hard matrix is likely to have a small ΔT value when formedinto a complex film. Therefore, by setting the glass transitiontemperature T_(g) high, as one method to decrease the value ΔT, heatresistance characteristics of the polymer dispersed liquid crystalcomplex film can be improved, whereby display characteristics areprevented from deterioration due to certain thermal circumstances.

The above-mentioned polymer dispersed liquid crystal complex filmaccording to the present invention is produced by subjecting the mixtureof the polymerizable material and the liquid crystal material to a phaseseparation process conducted through a polymerization reaction. Herein,the polymerizable material consists essentially of monofunctionalmonomers and either multifunctional monomers or multifunctionaloligomers. In this method, the phase separation process can easily becontrolled. Therefore, display characteristics of a resultant complexfilm are improved, whereby a low voltage operation, rapid electroopticalresponses, etc. are realized.

A polymer dispersed liquid crystal complex film having a desirable ΔTvalue, namely 10° C. or less, is produced in the following manner:Firstly, as is described above, the mixture is irradiated with light soas to effect a phase separation of the liquid crystal composition andthe polymer resin composition. Thereafter, the mixture which hasphase-separated is irradiated with light again but at a lowertemperature than in the first irradiation.

In this method, as is described above, the mixture which hasphase-separated is made to have a lower temperature in the secondirradiation of light than in the first irradiation of light. As aresult, a portion of the polymerizable material (such as monomers) whichremains unreacted, i.e. unpolymerized, and therefore is dissolved in theliquid crystal composition at the first irradiation of light comes outundissolved. By the second irradiation of light, the undissolved (andunreacted) portion of the polymerizable material is polymerized, wherebythe unreacted polymerizable material dissolved in the liquid crystalcomposition decreases in amount. As a result, the value ΔT can be made10° C. or less, according to this method.

In this method, the second irradiation should be conducted at,preferably, a temperature lower by 10° C. or more than in the firstirradiation, and at a crystallization temperature, or above, of theliquid crystal material included in the liquid crystal composition. Whenthe difference between the temperature at the first irradiation and thatat the second irradiation is less than 10° C., the state of phaseseparation after the second irradiation is not very different from thestate of phase separation after the first irradiation. As a result, theamount of the unreacted polymerizable material does not have such adecrease, that is, that effect of the present invention is not attained.When the second irradiation is conducted at the crystallizationtemperature of the liquid crystal material or below, phase separation isnot conducted sufficiently, since movements of materials are not likelyto occur. More preferably, in cases where a liquid crystal materialhaving a smectic phase between a nematic phase and an isotropic phase isused, e.g. when ferroelectric liquid crystal is used, the desirabletemperature range should be such that the liquid crystal shows a smecticphase. The reason is that liquid crystal is more orderly and less fluidat a smectic phase than at a nematic phase, and therefore is easilyoriented, making it easy to conduct phase separation at, in particular,the second irradiation.

As for orientation treatments suitably used in the present invention,for example, an organic film such as that made of polyimide or aninorganic film such as that made of SiO₂ can be formed on a surface of asubstrate, and if necessary, a rubbing method or the like can suitablybe used. Examples of polyimide are SE150 (manufactured by NissanChemical Industries Ltd.), Cytop (manufactured by Asahi Glass Co.,Ltd.), and the like.

The polymer-matrix type liquid crystal display device of the presentinvention includes a pair of electrode substrates and a display mediumconsisting essentially of a complex film interposed therebetween, Thedisplay medium includes the liquid crystal composition and the polymerresin composition. The liquid crystal composition forms liquid crystalregions that correspond to pixel regions, and is supported by a polymermatrix consisting of the polymer composition. Liquid crystal domains areoriented either radially or randomly in each liquid crystal region. Thisdisplay medium has a value ΔT of 25° C. or less, and a glass transitiontemperature of 50° C. or more.

This complex film has excellent viewing angle characteristics, and thereason therefor will be described with reference to FIGS. 3A and 3B.FIGS. 3A and 3B are cross-sectional views of a liquid crystal displaydevice in which the above-mentioned display medium is used. FIG. 3Adescribes a state where an intermediate gray tone is displayed, whileFIG. 3B describes a state where the display medium is transparent.

In a transparent state, as is shown in FIG. 3B, each liquid crystalmolecule 11 has the same apparent refractive index, irrespective of theviewing angle, as in a conventional display medium. However, in a statewhere the display medium is displaying an intermediate gray tone, as isshown in FIG. 3A, the liquid crystal molecules 11 standomnidirectionally when a voltage is applied to the display medium sothat an intermediate gray tone is displayed, since the liquid crystaldomains are oriented either radially or randomly in a liquid crystalregion 15 surrounded by a polymer matrix 14. Thus, the liquid crystalmolecules 11, as observed from a direction A, stand at the same angle asin cases where they are observed from a direction B. In other words, theapparent refractive index of liquid crystal molecules 11 as a whole doesnot depend on the viewing angle, whereby the viewing anglecharacteristics are improved.

Moreover, the value ΔT and the glass transition temperature T_(g) ofthis display medium are to be set within a similar range to thoseprescribed for the above-mentioned complex film. Therefore, this displaymedium (complex film) has as good display characteristics and heatresistance characteristics as the complex film mentioned earlier does.

An example of a method for producing a liquid crystal display device inwhich such a display medium is used will be described, with reference toFIGS. 4A and 4B.

First, as is shown in FIG. 4A, substrates 1 and 3 are disposed so as tooppose each other. On the substrate 1, strip-shaped electrodes 2 areformed so as to be parallel to one another. On the substrate 3,strip-shaped electrodes 4 are formed so as to be parallel to oneanother. Between the substrates 1 and 3, a mixture 5 of a polymerizablematerial and a liquid crystal material is sealed. The polymerizablematerial consists essentially of monofunctional monomers and at leastone of multifunctional monomers and multifunctional oligomers. Herein,each strip-shaped electrode 2 and each strip-shaped electrode 4 areperpendicular to each other. The mixture 5 may include a polymerizationinitiator, as will be described later.

Next, a glass plate 6, on which a photomask 7 is formed, is disposed onthe substrate 1. Then, the mixture 5 is irradiated with UV (UltraViolet)-rays 10 through the photomask 7. The photomask 7 is formed so asto have masking portions 7a corresponding to pixel regions of the liquidcrystal display device. This makes possible an irradiation of themixture 5 with UV-rays having a distribution of intensities withsubstantially identical regularity with that of desired liquid crystalregions (pixels). In a portion of the mixture 5 where UV-rays areradiated, namely a portion excluding the pixel regions, polymerizationoccurs rapidly. Therefore, the phase separation rate of the liquidcrystal composition and the polymer resin composition is high, so that apolymer that has deposited thrusts the liquid crystal to a portion whichis masked by the masking portion 7a, where the UV-rays have a lowintensity. At the same time, the polymerizable material (and thepolymerization initiator) gathers at a portion where polymerization istaking place, owing to a concentration gradient. As a result, as isshown in FIG. 4B, a polymer matrix 8 and liquid crystal regions 9 areclearly separated, the liquid crystal regions 9 being uniformly formedand regularly arranged so as to be on a plane.

In the steps of where irradiation with UV-rays is conducted, if themixture of the liquid crystal material and the polymerizable material ispolymerized in a liquid crystal state, an orientation of the mixture isstrongly controlled by a substrate, since a resultant polymer is also ina liquid crystal state. Herein, suitable liquid crystal phases are anematic phase and a smectic phase. In view of movements of materialssuch as the polymerizable material at the irradiation with UV-rays, anematic phase is preferable because of the high fluidity thereof.

In this method as well, an orientation treatment can be conducted byforming an organic film or an inorganic film on a surface of at leastone of the substrates, and if necessary, a rubbing method or the likecan be suitably used. Conducting an orientation treatment improvesorientational regularity of the liquid crystal domains, insulatingproperties, and adhesion between the display device and the substrates.

In a case where, as in the present method, a mixture of a liquid crystalmaterial and a photopolymerizable material is irradiated with lighthaving intensities ranging from high to low, a thin polymer film mayoccasionally be left on a surface of a substrate even in liquid crystalregions thereof. In this case, an orientation film formed on thesubstrate does not exercise a strong orientation control over the liquidcrystal regions. As a result, liquid crystal domains in each liquidcrystal region are oriented radially or randomly.

In a case where a vertical orientation film is used, which has a strongorientation control over liquid crystal regions, liquid crystalmolecules stand vertically with respect to a substrate, thusconstituting a homeotropic orientation. In this case, because of aninteraction between the liquid crystal molecules and a polymer matrix,the liquid crystal molecules stand in parallel with the substrate when avoltage is applied. As a result, the refractive index of each liquidcrystal molecule becomes substantially the same irrespective of theviewing angle, whereby viewing angle characteristics are improved.

It was confirmed that, in cases where a material having a strongorientation property such as ferroelectric liquid crystal is used,orientation of the liquid crystal regions can be conducted in accordancewith an orientation of the substrate even by the present method wherethe orientation control is weakened.

In the present method, in order to ensure that the pixel regions and theliquid crystal regions correspond to each other, it is important toacquire UV-rays having a distribution of intensities ranging from highto low. Other light regulating means can be used in place of aphotomask. For example, a microlens array, an interfering plate, etc.are preferable in that they are capable of forming a regulardistribution of UV-ray intensities.

In a case where a photomask is used, the photomask can be provided oneither the inside or outside of a substrate, as long as a regulardistribution of UV-ray intensities is obtained. The photomask shouldpreferably be as close to the mixture of the liquid crystal material andthe polymerizable material as possible. If the distance between thesubstrate and the photomask is made large, a portion of the mixture thatis actually irradiated with the UV-ray is blurred, therefore reducingthe effect of the present invention. Herein, UV-rays to be used shouldpreferably be parallel rays.

However, in cases where ferroelectric liquid crystal is used as theliquid crystal material, light with a slightly poorer degree ofparallelism can be used. The reason is that, in the case offerroelectric liquid crystal, shock resistance of the complex filmshould be improved, and therefore it is effective to provide smallerliquid crystal droplets as buffers at the periphery of each liquidcrystal region. Instead of using light with a slightly poorer degree ofparallelism, a light regulating means (such as a photomask) having ablurred end portion can be used. Alternatively, the photomask can alsobe placed at a distance from the mixture.

Regarding portions of the light regulating means (such as a photomask)for respectively forming a strongly-irradiated region andweakly-irradiated regions of the mixture, a study by the inventorsrevealed the following. In the case of a mode which does not utilizescattering of light between a polymer resin composition and a liquidcrystal composition, e.g. a non-scattering mode used in the presentexample, it is preferable that the size of each portion of the lightregulating means for forming a weakly-irradiated region (hereinafter,this portion will be referred to as a `masking portion`) accounts for30% or more of the area of each pixel. If, on the contrary, the size ofeach masking portion of the light regulating means is less than 30% ofthe area of each pixel, the size of a resultant liquid crystal region isalso less than 30% of the area of each pixel; this means that a numberof interfaces between a liquid crystal region and the polymer matrix arepresent in one pixel region, so that the contrast of the liquid crystaldevice lowers because of light scattering. Such a liquid crystal deviceis not practical. More preferably, a photomask or the like which allowsthe UV-ray to be radiated exclusively on portions of the mixtureexcluding the pixel regions should be used. In this case, the number ofinterfaces between a liquid crystal region and the polymer matrix whichare present in one pixel region becomes extremely small. As a result,the intensity of scattering of light in the pixel region decreases,whereby the contrast of the liquid crystal device can be improved.

Each masking portion can have any shape as long as the intensity of theUV-ray is locally lowered in 30% or more of the area of each pixelregion. For example, the configuration of each masking portion can be acircle, a square, a trapezoid, a hexagon, a rectangle, a diamond shape,a letter, or a shape surrounded by a curved line(s) and/or a straightline(s). A configuration obtained by cutting a part off these shapes, aconfiguration obtained by combining different shapes, a configurationobtained by combining the same shape, and the like can also be used.However, the shape of each masking portion is not limited to those whichare listed above. When the present invention is put to practical use,one or more of these shapes are to be selected. In order to improveuniformity of the liquid crystal regions, it is preferred to limit theconfiguration to one shape with one size.

Moreover, one masking portion can be provided for more than one pixel.For example, as is shown in FIG. 5A, each masking portion can beprovided for a row consisting of more than one pixel, or as is shown inFIG. 5B, for a group consisting of more than one pixel. Furthermore, themasking portions do not need to be independent from one another, but canbe connected to one another at an end portion, as long as portionsintercepting the UV-rays most effectively have one or more of theabove-mentioned configurations and/or arrangements. Preferably, thepitch of each liquid crystal region is made equal to that of each pixelregion, whereby one liquid crystal region is provided for each pixelregion.

In this method as well, a polymer dispersed liquid crystal complex filmhaving a desirable ΔT value, namely 10° C. or less, can be obtained byirradiating the mixture of the liquid crystal material and thepolymerizable material with light so as to effect a phase separation,and further irradiating the mixture, which has phase-separated, withlight but at a lower temperature than in the first irradiation. Herein,in order to protect the liquid crystal composition and to have bettercontrol of the configurations of the liquid crystal regions, a lightregulating means such as a photomask should be used at the secondirradiation as well as at the first irradiation.

Such a polymer-matrix type liquid crystal display device, however, hasthe problem of low contrast. Above all, a displayed image has a coarseappearance, as has been described earlier. In order to solve thisproblem, a study was conducted by the inventors of the presentinvention. The study revealed that a liquid crystal display devicehaving excellent viewing angle characteristics can be realized by usinga mixture of a liquid crystal material and a polymerizable materialwhich meet the following relationship, regarding a refractive indexn_(p) of a resultant polymer obtained through polymerization, and anordinary refractive index n_(o) and an extraordinary refractive indexn_(e) of the liquid crystal:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2

It was confirmed that a liquid crystal display device having excellentdisplay quality can be obtained by using such a mixture and selectivelycontrolling the distribution of liquid crystal regions and a polymermatrix through a phase separation process.

Hereinafter, the present invention will be further described, regardingthe above-mentioned effect.

A liquid crystal display device according to the present inventionincludes a plurality of pixels partitioned by a polymer matrix. Eachpixel has one or more liquid crystal domain. In cases where each pixelhas a plurality of liquid crystal domains, it is preferable that theliquid crystal domains have different orientations from one another. Incases where each pixel has one liquid crystal domain (i.e. in`monodomain` cases), the liquid crystal panel as a whole includes liquidcrystal domains having different orientations from one another. In otherwords, the whole liquid crystal panel includes liquid crystal domainshaving different orientations from one another in both cases. Moreover,in monodomain cases, each pixel has no disclination lines, which wouldusually appear as bright streaks that are disadvantageous to the displaycharacteristics of the display device. Therefore, the contrast of such amonodomain liquid crystal display device is improved.

When a voltage is applied to the liquid crystal display device(monodomain or otherwise), liquid crystal molecules in each liquidcrystal region stand vertically with respect to substrates; thereforeeach liquid crystal molecule has a refractive index n_(o). When novoltage is applied, the liquid crystal molecules are oriented so as tobe parallel to the substrates; therefore, each liquid crystal moleculehas a refractive index (n_(e) +n_(o))/2 with respect to light incidentthereto. A main objective of the present invention is to improve thecontrast of the liquid crystal display device and especially to minimizethe coarseness problem of a displayed image by restraining thescattering of light occuring due to a difference in refractive indicesof the liquid crystal and the polymer matrix. This objective is met byensuring that a refractive index n_(p) of the polymer falls within arange between the ordinary refractive index n_(o) of each liquid crystalmolecule and the refractive index (n_(e) +n_(o))/2 of each liquidcrystal molecule in a randomly oriented state, so as to minimize thedifference in the refractive indices of the liquid crystal and thepolymer. Herein, however, it was confirmed by a study by the inventorsthat the above-mentioned objective of improving the contrast of thedisplay device can be met as long as the difference between therefractive index n_(p) of the polymer and the ordinary refractive indexn_(o) of each liquid crystal molecule is 0.04 or less. Hereinafter, thiseffect of improvement of contrast will be described with reference toFIG. 17.

When a contrast ratio CR is defined as a ratio of a transmittanceT_(OFF) under no voltage applied to a transmittance T_(ON) under avoltage applied (i.e. when CR=T_(OFF) /T_(ON)), it is very effective toreduce the transmittance T_(ON) in order to improve the contrast of theliquid crystal display device. Therefore, the inventors examined how thetransmittance T_(ON) is affected when the refractive index n_(p) of thepolymer is varied in the vicinity of the ordinary refractive index n_(o)of each liquid crystal molecule. FIG. 17 illustrates the results of theabove examination. As is seen from FIG. 17, the transmittance T_(ON)under a voltage applied decreases as the difference between therefractive index n_(p) of the polymer and the ordinary refractive indexn_(o) of each liquid crystal molecule decreases. When the value |n_(o)-n_(p) | is 0.04 or less, the transmittance T_(ON) is 1% or less;accordingly, the contrast ratio CR as defined above is greatlyincreased. On the other hand, when the value |n_(o) -n_(p) | is morethan 0.04, the transmittance T_(ON) is more than 1%; accordingly, thecontrast ratio CR decreases.

As for the range of the difference in the refractive indices of theliquid crystal and the polymer, the following facts are observed, withreference to FIG. 15:

(A) When the refractive index n_(p) of the polymer is smaller than [theordinary refractive index n_(o) of the liquid crystal-0.04], therefractive index n_(p) and the refractive index (n_(e) +n_(o))/2 of theliquid crystal in a randomly oriented state have a large difference.Therefore, the coarseness problem when no voltage is applied worsens.

(B) When the refractive index n_(p) of the polymer matrix is larger thanthe refractive index (n_(e) +n_(o))/2 of the liquid crystal in arandomly oriented state, the refractive index n_(p) and the ordinaryrefractive index n_(o) of the liquid crystal have a large difference.Therefore, the coarseness problem when a voltage is applied worsens.

(C) By ensuring that the refractive index n_(p) of the polymer matrix isin a range between [the ordinary refractive index n_(o) of the liquidcrystal-0.04] and the refractive index (n_(e) +n_(o)) /2 of the liquidcrystal in a randomly oriented state, the difference between therefractive index of the liquid crystal and that of the polymer matrix(i.e. n_(p)) can be made small in both of i) cases where a voltage isapplied (that is to say, the difference between the ordinary refractiveindex n_(o) of the liquid crystal and the refractive index n_(p) of thepolymer matrix is small) and ii) cases where no voltage is applied (thatis to say, the difference between the refractive index (n_(e) +n_(o))/2of the liquid crystal in a randomly oriented state and the refractiveindex n_(p) of the polymer matrix is small).

Moreover, the difference between the refractive index of the liquidcrystal and that of the polymer matrix can be made to vary within only asmall range in spite of changes in voltage between a state where avoltage is applied and a state where no voltage is applied.

Thus, the contrast of the liquid crystal display device is improved, andthe coarseness problem of a displayed image can be minimized.

Hereinafter, the polymerizable material and the liquid crystal materialto be used in the present invention will be described.

First, the polymerizable material, which is polymerized to form thepolymer resin composition, will be described. The polymer polymerizablematerial is a precursor for forming the polymer dispersed liquid crystalcomplex film and the above-mentioned liquid crystal display device, andcan be a photopolymerizable material, a thermosetting material, or thelike. In the case of a photopolymerizable material, for example, it is aphotopolymerizable one of mixtures including a monofunctional monomerand at least one of a multifunctional monomer and an oligomer thereof;and occasionally a polymerizable fluorine-containing resin compound, apolymerizable chlorine-containing resin compound, and/or a polymerizablesilicon-containing resin compound. The mixture may, if necessary,further include one or more surfactants.

The polymerizable material as cited herein means a substance including acompound whose molecules include a reactive double bond and/or afunctional group such as an epoxy group. In particular, aphotopolymerizable material means a substance including an acrylatemonomer (oligomer), methacrylate monomer (oligomer), or the like. It isvery effective to ensure that, in order to raise the glass transitiontemperature T_(g) of the polymer composition so as to form a hard matrixand in order also to realize a high voltage-holding ratio, the substanceincludes a resin compound containing fluorine, chlorine, or silicon.

Herein, an example mixing ratio of the monofunctional monomer to themultifunctional monomer and oligomer in the polymerizable material to beused in the present invention is, by weight, 93:7 to 40:60. Moreover, aglass transition temperature T_(g) of a polymer obtained by polymerizingand curing such a polymerizable material should be 60° C. or more, andmore preferably, in the range of 80° C. to 180° C. If the monofunctionalmonomer accounts for a larger portion in the mixing ratio of thepolymerizable material, physical strength of a resultant polymer matrixis not sufficient in terms of practicality. Moreover, the diameters ofthe dispersed liquid crystal grains increase because a sufficientpolymerization/phase separation rate cannot be obtained. Therefore,contrast of the liquid crystal device lowers considerably. If themonofunctional monomer accounts for a smaller portion than theprescribed range, on the other hand, compatibility of the liquid crystalcomposition and the polymer resin composition lowers, making itdifficult to produce a polymer dispersed liquid crystal display devicecapable of operating at a low voltage.

In a case where a polymerizable fluorine-containing resin compound, apolymerizable chlorine-containing resin compound, a polymerizablesilicon-containing resin compound, and/or a surfactant is added to thepolymerizable material, those compounds should account for, by weight,1% to 50% of the polymerizable material, and more preferably, 5% to 40%of the polymerizable material. Herein, if the polymerizablefluorine-containing resin compound, polymerizable chlorine-containingresin compound, and polymerizable silicon-containing resin compoundaccount for a smaller portion of the polymerizable material than theabove, the superficial energy of a resultant polymer is not sufficientlylow. If these polymerizable compounds account for a larger portion, onthe other hand, it becomes difficult to obtain a homogeneous mixure ofthe liquid crystal material and the polymerizable material. As a result,a uniformly-formed polymer dispersed liquid crystal complex film cannotbe obtained, and the glass transition temperature T_(g) of the polymerincluded in the complex film or the polymer-matrix type display devicedecreases.

Transparent fluorine-containing compound, chlorine-containing compound,and silicon-containing compound to be used should have only a smalldegree of polarization and generate few ions. They should be chemicallyinactive, and have excellent dielectric characteristics and relativelyhigh insulative property. In this case, the superficial energy of aresultant polymer is lowered so that an interaction at an interfacebetween the liquid crystal and the polymer is reduced, whereby theresponse speed of the liquid crystal device is improved, and thevoltage-transmittance hysteresis thereof is reduced.

In the case of a photopolymerizable material, the glass transitiontemperature T_(g) of the monofunctional monomer to be mixed with afluorine monomer, a chlorine monomer, and/or a silicon monomer should be10° C. or more, and more preferably, 30° C. or more.

However, even in the case where a monofunctional monomer whose glasstransition temperature T_(g) is in the vicinity of 0° C. is used, byadding a multifunctional and/or monomer or oligomer, the glasstransition temperature T_(g) of a resultant polymer can be raised to 60°C. or more. However again, in the case of a resin compound whose glasstransition temperature T_(g) is 10° C. or less, this effect of improvingthe glass transition temperature T_(g) of a resultant polymer isreduced.

As for the multifunctional monomer and multifunctional oligomer to beused, those having a glass transition temperature T_(g) of at least 60°C. or more are preferable. This multifunctional monomer, as comparedwith the monofunctional oligomer, has an effect of lowering thetemperature at which it is compatible with the liquid crystal, and themolecular weight thereof should be 1000 or less. The more functionalgroups the multifunctional monomer has, the more it raises the glasstransition temperature T_(g).

Moreover, a multifunctional monomer and a multifunctional oligomer havea number of reactive cites in polymerization reactions and thereforetend to form a polymer matrix having a harder three-dimensional netstructure. As a result, a small amount of impurities which may possiblyremain after production of the polymer dispersed liquid crystal complexfilm are prevented from moving, whereby the voltage-holding ratio of theliquid crystal display device is raised.

Hereinafter, examples of polymerizable materials (monofunctionalmonomers, multifunctional monomers and multifunctional oligomers) to beused so that the value ΔT falls within the above-prescribed range, andformulas of fluorine-containing resin compounds, chlorine-containingcompounds, or silicon-containing compounds, which may be further addedin order to improve display characteristics of the liquid crystaldevice, will be described.

A case will be described where a photopolymerizable material is used.

Examples of monofunctional monomers are: cyclohexyl acrylate (Tg: 16°C.), dicyclopentenyloxyethyl acrylate (T_(g) : 12° C.),tetrahydrofurfuryl acrylate (T_(g) : 60° C.), dicyclopentenyl acrylate(T_(g) : 95° C.), isobornyl acrylate (T_(g) : 90° to 100° C.),t-butylaminoethyl methacrylate (T_(g) : 33° C.), dicyclopentenyloxyethylmethacrylate (T_(g) : 30° C.), stearyl methacrylate (T_(g) : 38° C.),glycidyl methacrylate (T_(g) : 41° C.), 2-hydroxyethyl methacrylate(T_(g) : 55° C.), cyclohexylmethacrylate (T_(g) : 66° C.), isobornylmethacrylate (T_(g) : 170° C.), and the like.

Examples of multifunctional monomers are: neopentylglycol diacrylate(T_(g) : 70° C.), bisphenol A diethoxy diacrylate (T_(g) : 75° C.),tripropyleneglycol diacrylate (T_(g) : 90° C.),propoxytrimethylolpropane tryacrylate (T_(g) : 120° C.), pentaerythritoltriacrylate (T_(g) : >250° C.), trimethylolpropane triacrylate (T_(g): >250° C.), dipentaerythritol hexaacrylate (T_(g) : >250° C.), and thelike.

Examples of fluorine-containing resin compounds are those which arerepresented by the following Formula I: ##STR1## (wherein R₁ representsH or CH₃ ; R₂ represents C_(n1) F_(2n1+1) ; n1 is an integer of 1 to 5;and m1 is an integer of 1 to 21.)

Examples of chlorine-containing resin compounds are those which arerepresented by the following Formula II: ##STR2## (wherein R₃ representsH or CH₃ ; R₄ represents C_(n2) Cl_(2n2+1) ; n2 is an integer of 1 to 5;and m2 is an integer of 1 to 21.)

Examples of silicon-containing compounds are those which are representedby the following Formula III: ##STR3## (wherein R₅ represents H or CH₃ :n3 is an integer of 1 to 5; and m3 is an integer of 1 to 10), or thosewhich are represented by the following Formula IV: ##STR4## (wherein Xrepresents Si(OC_(s) H_(2s+1))₃, Si--CH₃ (OC_(s) H_(2s+1))₂, orSi--(CH₃)₂ OC_(s) H_(2s+1) ; q is an integer of 1 to 5; and s is aninteger of 1 to 3). More specifically, there are vinylalkoxysilanecompounds such as vinyltris (β-methoxyethoxy)silane,vinyltriethoxysilane, and vinyltrimethoxysilane.

A polymer material to form a polymer resin composition used in thepresent example is required to have high stability against heat and highelectric resistance characteristics. In particular, in cases where thepolymer dispersed liquid crystal complex film is used for a liquidcrystal display device and is driven by an active matrix system such asthat using a TFT (Thin Film Transistor), it is necessary for the liquidcrystal display device to have excellent voltage-holding ratiocharacteristics. This requires, however, that the polymer material issufficiently refined so as to have a specific resistance of 10¹² Ω·cm ormore. As for a photopolymerizable material, for example, an acrylic acidand an acrylic acid ester having a benzene ring or a long-chain alkylgroup having three or more carbons can be used.

More specifically, besides the above-mentioned compounds, isobutylacrylate, stearyl acrylate, lauryl acrylate, isoamyl acrylate,n-butylmethacrylate, n-lauryl methacrylate, tridecyl methacrylate,2-ethylhexyl acrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate,and the like can be used.

In order to increase the physical strength of the resultant polymerresin composition, multifunctional compounds having two or morefunctional groups, such as bisphenol A dimethacrylate, bisphenol Adiacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanedioldimethacrylate, trimethylol propane trimethacrylate,tetramethylolmethane tetraacrylate, and neopentyl diacrylate, can beused.

More preferably, compounds obtained by halogenating, in particular bychlorinating or fluorinating, some of the above-mentioned monomers canbe used. Examples of such compounds include 2,2,3,4,4,4-hexaphlorobutylmethacrylate; 2,2,3,4,4,4-hexachlorobutyl methacrylate;2,2,3,3-tetraphloropropyl methacrylate; 2,2,3,3-tetraphloropropylmethacrylate; perphlorooctyl methacrylate; perchlorooctylethylmethacrylate; perphlorooctylethyl acrylate; and perchlorooctylethylacrylate.

When a photomask is used, in order to form liquid crystal regions inaccordance with configurations of masking portions of the photomask, itis preferable to add a substance for restraining the polymerizationreaction to the above-mentioned polymerizable materials. Such substancesare, more specifically, monomers or compounds, etc. which stabilize aradical by a resonance system after the radical has been produced. Forexample, there are styrene, p-chlorostyrene, p-methylstyrene, p-phenylstyrene, 4-vinylnaphthalene, nitrobenzene, and the like.

Hereinafter, the liquid crystal material included in the liquid crystalcomposition of the present invention, will be described.

The liquid crystal used in the present invention is an organic compoundor organic mixture which is generally in liquid crystal state in thevicinity of room temperature, and includes nematic liquid crystal(including liquid crystal for double channel drive and liquid crystalwhose anisotropy Δε of dielectric constant is less than 0), cholestericliquid crystal, smectic liquid crystal, ferroelectric liquid crystal,discotic liquid crystal, and the like. These liquid crystal materialsmay be a mixture of two or more kinds of liquid crystal compounds. It ispossible to construct a guest-host mode liquid crystal display deviceusing such a liquid crystal material with one or more kinds of dichroicdyes further included therein. Herein, in terms of compatibility, it isalso preferable to use, as the polymerizable material, a compound inwhich a liquid-crystallinity exhibiting portion is introduced to apolymerizable functional group, which serves as a polymerizable liquidcrystal prepolymer. In that case, use of liquid crystal materialscontaining fluorine or chlorine requires that the liquid crystalcompound having a polymerizable functional group also contains fluorineor chlorine, because of idiosyncratic chemical circumstances pertainingto the liquid crystal materials containing fluorine or chlorine. Incases where ferroelectric liquid crystal is used, it is also preferableto use a polymerizable liquid crystal prepolymer in order to form astable smectic phase.

Examples of polymerizable functional groups are functional groups suchas acryloyl, methacryloyl, and epoxy (glycidyl)groups. Examples of suchpolymerizable liquid crystal prepolymers are disclosed in JapaneseLaid-Open Patent Publication Nos. 62-277412, 63-264629, 63-280742, andthe like. Such liquid crystal prepolymers can be added to the liquidcrystal material unless they undermine display characteristics of theliquid crystal display device.

A polymerizable liquid crystal prepolymer means, though the presentinvention intends to provide no limitations thereto, such a compound asrepresented by the following Formula V, and is a compound which is notlikely to affect liquid crystallinity of host liquid crystal molecules.

    A--B--LC                                                   Formula V

In Formula V, A represents a polymerizable functional group. Examplesthereof include functional groups having unsaturated bonds such as CH₂═CH--, CH₂ ═CH--COO--, CH₂ ═C(CH₃)--COO--, and --N═C═O, and functionalgroups having a heterocyclic structure with strain such as a structurerepresented by the following Formula VI. ##STR5##

B represents a coupling group connecting the polymerizable functionalgroup to the liquid crystalline compound. Examples thereof include analkyl chain (--(CH₂)_(n) --), an ester bond (--COO--), an ether bond(--O--), a polyethylene glycol chain (--CH₂ CH₂ O--), and other couplinggroups obtained by combining these coupling groups. In particular, inorder that the compound represented by Formula V shows liquidcrystallinity when mixed with the liquid crystal material, a couplinggroup having 6 or more bonds from the polymerizable functional group tothe fixed portion of the liquid crystal molecules is preferred.

LC represents a liquid crystalline compound. Examples thereof include acompound represented by the following Formula VII, a cholesterol ring,and derivatives thereof.

    D--E--G                                                    Formula VII

In Formula VII, D represents a functional group capable of being boundto the coupling group represented by the letter B, and has a function ofinfluencing the value of anisotropy of dielectric constant of the liquidcrystal molecules and that of the anisotropy of refractive index.Examples thereof include a paraphenyl ring, a 1,10-diphenyl ring, a1,4-cyclohexane ring, a 1,10-phenylcyclohexane ring, a naphthalene ring,and a tarphenyl ring. G represents a polar group which causes theanisotropy of dielectric constant, etc. of the liquid crystal to beexhibited. Examples thereof include a benzene ring, a cyclohexane ring,a paradiphenyl ring, and a phenylcyclohexane ring, each having afunctional group such as --CN, --OCH₃, --F, --Cl, --OCF₃, --OCCl₃, --H,--R (R: alkyl group). E represents a functional group ,connecting D toG. Examples thereof include a single bond, --CH₂ --, --CH₂ CH₂ --,--O--, --C.tbd.C--, and --CH═CH--.

The liquid crystal material and the polymerizable material shouldpreferably constitute a ratio in the range of, by weight, 50:50 to 93:7,and more preferably, 70:30 to 90:10, when mixed together. If the liquidcrystal material accounts for less than 50%, the polymer matrix has moreinfluence, so that the driving voltage of the liquid crystal devicebecomes extremely large, therefore ruining practicality of the liquidcrystal device. If the liquid crystal accounts for more than 93%, on theother hand, the physical strength of the polymer matrix lowers, so thatthe liquid crystal device cannot have stable performance.

Moreover, in cases where a compound having liquid-crystallinity and apolymerizable material having no liquid-crystallinity are mixed to formthe polymer material, the compound having liquid-crystallinity shouldaccount for 0.5% or more of the polymerizable material. Herein, thepolymer material as a whole (consisting of the compound havingliquid-crystallinity and the polymerizable material having noliquid-crystallinity) and the liquid crystal material should also meetthe prescribed mixing ratio mentioned above. In a case where dielectricliquid crystal is used, in particular, the compound havingliquid-crystallinity may account for 100% of the polymerizable material,so that two regions consisting of liquid crystal having a smallmolecular weight and liquid crystal having a large molecular weight areformed. By applying two voltages each corresponding to a driving voltagefor the former region (consisting of liquid crystal having a smallmolecular weight) and a driving voltage for the latter region(consisting of liquid crystal having a large molecular weight) to such aliquid crystal device in a controlled manner, a dielectric liquidcrystal display device capable of displaying tones of different levelscan be realized.

Moreover, the liquid crystal material to be used in the presentinvention should preferably be a chemically stable liquid crystalmaterial which includes a liquid crystal material containing fluorine orchlorine and shows a positive anisotropy of dielectric constant.Examples of such liquid crystal materials are, though not limited towhat is listed herein, ZLI-4801-1000, ZLI-4801-001, ZLI-4792 (allmanufactured by Merck & Co., Inc.), and the like. Liquid crystalmaterials which do not contain fluorine or chlorine, for example, thosewhich contain cyanobiphenyl, pyrimidine compounds, or the like, areinferior in terms of voltage-holding ratio characteristics,heat-resistance reliability, light-resistance reliability, etc.

Moreover, it is preferable that the liquid crystal material to be usedin the present invention is such that the a phase transition temperatureT_(NI) between a liquid crystal phase and an isotropic liquid phasethereof is 80° C. to 120° C. If the phase transition temperature T_(NI)is less than 80° C., heat resistance characteristics of the liquidcrystal device deteriorate, and the operational temperature range of theliquid crystal device lowers. Therefore, The practicality of the liquidcrystal device decreases. If the phase transition temperature T_(NI) ismore than 120° C., on the other hand, a compatible temperature of theliquid crystal material and the polymer resin composition increases,therefore making it very hard to produce a uniformly-formed liquidcrystal panel.

It is necessary that the liquid crystal material to be used issufficiently refined so as to have a specific resistance of 10¹² Ω·cm ormore, and preferably that of 10¹³ Ω·cm or more.

It is also effective to add an optically active chiral dopant and/orcholesteric liquid crystal to the liquid crystal material. Morespecifically, a cholesteric phase emerges because of the presence of thechiral dopant; in cases where a helical pitch of the liquid crystal isidentical with a wavelength of light in a visible wavelength range, forexample, it therefore becomes possible to control between selectivelyreflecting light corresponding to the helical pitch of the liquidcrystal, displaying a transparent state, or a light-scattering states,by turning on and off an electrical field. It is always expected thatdisplay characteristics of the liquid crystal device are improved owingto a twisting force of a focal conic generated due to the addition ofthe chiral dopant.

The chiral dopant and/or the cholesteric liquid crystal to be usedshould preferably be, if at all, added to the liquid crystal material ata ratio in a range of 0.1% to 5%, and more preferably 0.1% to 2%, withrespect to the liquid crystal material. If a smaller ratio of the chiraldopant and/or the cholesteric liquid crystal than this range is added tothe liquid crystal material, the effect of improving displaycharacteristics of the liquid crystal device is reduced. If a largerratio of the chiral dopant and/or the cholesteric liquid crystal thanthis range is added to the liquid crystal material, on the other hand,it leads to a large hysteresis, and the voltage-holding ratiocharacteristics of the liquid crystal device tend to worsen.

Moreover, it is possible to improve contrast of the liquid crystaldevice or to realize a multicolor liquid crystal device by ensuring thatthe liquid crystal includes one or more kinds of dichroic dyes, owing toa light-absorption effect. The dichroic dye(s) to be used shouldpreferably be, if at all, added to the liquid crystal material at aratio, by weight, in a range of 0.5% to 10%, and more preferably 1% to5%, with respect to the liquid crystal material. If a smaller ratio ofthe dichroic dye(s) than this range is added to the liquid crystalmaterial, a sufficient effect does not result from the addition thereof.If a larger ratio of the dichroic dye(s) than this range is added to theliquid crystal material, on the other hand, display characteristics(such as voltage-holding ratio characteristics, response speed, andvoltage-transmittance hysteresis) of the liquid crystal devicedeteriorate.

Hereinafter, polymerization initiators to be optionally added to themixture of the polymerizable material and the liquid crystal materialwill be described.

Compounds used in paints, adhesives, etc. can be used as apolymerization initiator. Examples of polymerization initiators are:Irgacure 651, Irgacure 184, Irgacure 907 (all manufactured by:CIBA-GEIGY Corporation), Darocure 1173, Darocure 1116, Darocure 2956(all manufactured by: S. Merck & Co., Inc.), and the like.

As for the amount of such a polymerization initiator to be added, itdepends on reactiveness of the individual compound, so the presentinvention provides no particular prescription. In the case of aphotopolymerization initiator, however, it should preferably be, if atall, added to the mixture of the liquid crystal material and thephotopolymerizable material (including a polymerizable liquid crystalprepolymer) at a ratio of 0.01% to 5%, with respect to the mixture. Ifthe photopolymerization initiator accounts for more than 5%, the phaseseparation rate of the liquid crystal composition and the polymer resincomposition is so high that it becomes impossible to control the sizesof the liquid crystal regions, therefore creating the followingproblems: Since liquid crystal droplets are small, the liquid crystaldevice requires a high driving voltage, and an orientation film on asubstrate has a weak orientation control over, the liquid crystalregions. Moreover, liquid crystal regions which are present within pixelregions decrease in number because liquid crystal droplets formed inweakly-irradiated regions become small in cases where a photomask isused. As a result, contrast of the liquid crystal device decreases. Ifthe photopolymerization initiator accounts for less than 0.05%, on theother hand, a sufficient polymerization reaction cannot be conducted.

Moreover, a hardening accelerator can be added in order to prompt thepolymerization reaction, if necessary.

The polymer dispersed liquid crystal complex film can be, for example,applied to a liquid crystal display device as shown in FIGS. 6 and 7.This liquid crystal display device includes an electrode substrate fordisplaying purposes and a counter electrode substrate, between which adisplay medium 28 using the polymer dispersed liquid crystal complexfilm of the present example is interposed. The electrode substrate fordisplaying purposes, which is of an active matrix driving system,includes pixel electrodes 25 and switching transistors 24 eachcorresponding to each pixel electrode 25 as well as bus lines such assignal lines 22, scanning lines 23, etc. formed on a transparentinsulating substrate 21 made of glass having no birefringence. Thesignal lines 22, scanning lines 23, pixel electrodes 25, and theswitching transistors 24 are arranged in a matrix shape.

As the switching transistors 24, a-Si TFTs and the like are formed. Thecounter electrode substrate includes counter electrodes 27 formed on atransparent insulating substrate 26 made of glass, each counterelectrode 27 formed so as to correspond to each pixel electrode 25 ofthe electrode substrate for displaying purposes. The above-mentionedpixel electrodes 25 and the counter electrodes 27 are transparentelectrodes for applying a voltage to the display medium 28, and are madeof ITO (Indium Tin Oxide). The display medium 28 is sealed by a seal 29consisting of epoxy resin and the like.

The driving system and the configuration of the polymer dispersed liquidcrystal device are not limited to the above-mentioned active matrixdriving system using TFTs, but an active matrix drivingsystem/configuration using MIMs (Metal-Insulator-Metals), or a simplematrix driving system/configuration can alternatively be used. Moreover,the electrode substrates can alternatively be made of a plastic film,etc. instead of glass, so that the liquid crystal device has a smallerweight and requires lower manufacturing costs.

By providing two polarizing plates for the liquid crystal device of theabove-mentioned configuration, the two polarizing plates being disposedin a crossed-Nicol state, liquid crystal display devices having highcontrast and steep driving voltage characteristics, for example, aliquid crystal display device of a TN mode, an STN mode, an ECB mode, aguest-host mode, and a ferroelectric liquid crystal display device canbe produced.

Alternatively, only one polarizing plate may be provided for either oneof the substrates. For example, a reflector may be formed on the back ofa liquid crystal cell, or a liquid crystal material added with adichroic dye may be used. In this case, light is extracted at a greaterefficiency so that a brighter display can be obtained as compared to thecase where two polarizing plates are used.

A liquid crystal device which uses the polymer dispersed liquid crystalcomplex film of the present invention can alternatively have aconfiguration in which liquid crystal of an FLC (SSF) mode or an ECBmode, which are conventional display modes, is contained in or partiallypartitioned by the polymer matrix. This makes it possible to realize alarger display and to use films for the substrates instead of glass.

Hereinafter, the present invention will be described by way of examples.However, the scope of the present invention is not to be limitedthereto.

EXAMPLE 1

As Example 1 of the present invention, a liquid crystal display devicewas fabricated as follows:

First, a homogeneous mixture containing a photopolymerizable materialconsisting of 0.02 g of a bifunctional acrylate monomer (R-684,manufactured by Nippon Kayaku K.K.) and 0.18 g of isobornyl acrylate;0.78 g of a liquid crystal material (ZLI-4792, manufactured by Merck &Co., Inc.); and 0.039 of a photopolymerization initiator (Irgacure 651,manufactured by CIBA-GEIGY Corporation) was prepared.

Next, a cell was formed using two glass plates (flint glass with ITOhaving a thickness of 500 Angstroms, manufactured by Nippon Sheet GlassCo., Ltd.) with spacers each having a diameter of 12 μm interposedtherebetween. The two glass plates serve as substrates, while the ITO oneach glass plate serves as an electrode. Then, the above-mentionedmixture was injected into the cell.

Then, the cell was irradiated with UV-rays by using a high-pressuremercury lamp at an illuminance of 50 mW/cm² (at 365 nm; measured byUIT-101: a UV illuminometer manufactured by USHIO INC.) for 60 secondsto conduct photopolymerization. Thus, phase separation of the liquidcrystal composition and the polymer composition was conducted so as toform a polymer dispersed liquid crystal complex film.

A value ΔT and a glass transition temperature T_(g) of a liquid crystaldisplay device thus obtained were measured by the method(s) describedearlier.

Voltage-holding rate HR of the liquid crystal display device at roomtemperature was measured by an apparatus for measuring a voltage-holdingratio shown in FIG. 8. The apparatus, as is shown in FIG. 8, includes aswitching transistor (FET) for applying a voltage between electrodes ofa liquid crystal device, a driving circuit, and a circuit for measuringthe amount of discharged of electric charges stored in a liquid crystalcell of the liquid crystal display device.

Moreover, regarding electrooptical characteristics(voltage-transmittance characteristics) of the liquid crystal displaydevice, the following values were measured. First, a light transmittanceT₀ under no voltage applied, a light transmittance T₁₀₀ under analternating voltage of 50 V applied, and a response time τd required forthe light transmittance to vary by 90% after a voltage is stopped beingapplied were measured. Moreover, a value ΔV/V₅₀ obtained by normalizinga voltage-transmittance hysteresis width ΔV by an intermediate gray tonevoltage V₅₀ was measured. Then, a threshold voltage V_(th) and asaturation voltage V_(s) were measured. The threshold voltage V_(th) isdefined as an applied voltage when the light transmittance of the liquidcrystal device was increased by 10% of a value obtained by subtractingthe above-defined light transmittance T₀ from a saturation transmittanceT_(s) under an excess voltage applied. The saturation voltage V_(s) isdefined as an applied voltage when the light transmittance was increasedby 90% of the value obtained by subtracting the transmittance T₀ fromthe saturation transmittance T_(s) under an excess voltage applied. (Anoptical system was used in which a converging angle with respect to alight source thereof was 6° C.) Results of these measurements are listedin Table 1.

EXAMPLES 2 AND 3, and Comparative Example 1

Polymer dispersed liquid crystal display devices according to Examples 2and 3 of the present invention, and a liquid crystal display device asComparative Example 1 were fabricated as follows:

A mixture including a photopolymerizable material and a liquid crystalmaterial was prepared in each of Examples 2 and 3 and ComparativeExample 1. As the photopolymerizable material, 0.02 g oftrimethylolpropane triacrylate and 0.17 g of isobornyl acrylate wereused in each of Examples 2 and 3 and Comparative Example 1. As theliquid crystal material, 0.78 g of a fluorine-containing liquid crystalmaterial (ZLI-4801-000, manufactured by Merck & Co., Inc.), 0.78 g of afluorine-chlorine-containing liquid crystal material (TL-202,manufactured by Merck & Co., Inc.), and 0.78 g of acyanobiphenyl-containing liquid crystal material (E-8, manufactured byMerck & Co., Inc.) were used, respectively, in Examples 2 and 3 andComparative Example 1. The liquid crystal display devices werefabricated using the above-mentioned mixtures, by the same method asthat in Example 1.

Similar measurements to Those in Example 1 were taken with respect toeach liquid crystal display device; results of the measurements arelisted in Table 1. Electrooptical characteristics of each liquid crystaldevice at room temperature, after a liquid crystal cell thereof washeated at 80° C. for an hour, are listed in Table 2.

The liquid crystal devices of Examples 2 and 3 and Comparative Example 1include a polymer resin composition having a relatively high glasstransition temperature T_(g). The liquid crystal devices of Examples 2and 3, which use the fluorine-containing liquid crystal material, do notinclude: a cyano group, a pyrimidine ring, or the like, which are likelyto gather impurities. Therefore, the liquid crystal devices of Examples2 and 3 have a high voltage-holding ratio. Moreover, the liquid crystalmaterial used in the liquid crystal device of Example 3 containschlorine as well, and therefore has a large anisotropy Δn of refractiveindex, so that the light transmittance T₀ under no voltage applied issmaller than in the case of Example 2. As a result, a contrast ratioT₁₀₀ /T₀ thereof was greatly improved.

The liquid crystal device of Comparative Example 1, on the other hand,uses the cyanobiphenyl-containing liquid crystal material. Therefore,the voltage-holding ratio of the liquid crystal cell thereof isinsufficient as compared with those of Examples 1, 2, and 3, indicatingthat the liquid crystal device of Comparative Example 1 has smallpracticality. Moreover, as is seen from Table 2, the liquid crystaldisplay devices of Examples 2 and 3 show substantially no decrease incontrast thereof after being heated for an hour, as compared with adecrease in contrast of the liquid crystal of Comparative Example 1.This indicates that the liquid crystal devices of Examples 2 and 3 haveexcellent heat resistance characteristics. Furthermore, it can be seenthat the response time τd is greatly shortened in Examples 1, 2, and 3,as compared with that in Comparative Example 1.

Comparative Example 2

As Comparative Example 2, a polymer dispersed liquid crystal displaydevice was fabricated as follows:

A homogeneous mixture containing 0.78 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.); and a photopolymerizablematerial consisting of 0.02 g of a bifunctional acrylate monomer (R-684,manufactured by Nippon Kayaku K.K.) and 0.17 g of 2-ethylhexyl acrylate(Tg: -55° C.) was prepared. The liquid crystal device was fabricatedusing the above-mentioned mixture, by the same method as that in Example1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

Comparative Example 3

As Comparative Example 3, polymer dispersed liquid crystal displaydevice was fabricated as follows:

A homogeneous mixture containing 0.78 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.); and a photopolymerizablematerial consisting of 0.02 g of trimethylol propane triacrylate, 0.06 gof n-lauryl acrylate (Tg: -30° C.), and 0.11 g of 2-ethylhexyl acrylatewas prepared. The liquid crystal display device was fabricated using theabove-mentioned mixture, by the same method as that used in Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

As is seen from Table 1, the liquid crystal devices of ComparativeExamples 2 and 3 use a monomer(s) having a low glass transitiontemperature T_(g) as a main content of the polymerizable materialsthereof. Therefore, the value ΔT is large in both cases, indicative ofinsufficient electrooptical characteristics and heat resistance.

EXAMPLE 4

As Example 4 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing a photopolymerizable materialconsisting of 0.02 g of a bifunctional acrylate monomer (R-684,manufactured by Nippon Kayaku K.K.), 0.15 g of isobornyl acrylate, and0.03 g of a fluorine-containing monomer consisting ofβ-(perfluorooctyl)ethyl acrylate; 0.78 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.); and 0.03 g of aphotopolymerization initiator (Irgacure 651, manufactured by CIBA-GEIGYCorporation) was prepared. The liquid crystal display device wasfabricated using the above-mentioned mixture, by the same method as thatin Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

EXAMPLE 5

As Example 5 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing a photopolymerizable materialconsisting of 0.02 g of a bifunctional acrylate monomer (R-684,manufactured by Nippon Kayaku K.K.), 0.15 g of isobornyl acrylate, and0.03 g of a silicon-containing monomer (KBM 503, manufactured byShin-Etsu Chemical Co., Ltd.); and 0.78 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.) was prepared. The liquidcrystal display device was fabricated using the above-mentioned mixture,by the same method as that in Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

EXAMPLES 6 AND 7, and Comparative Example 4

Polymer dispersed liquid crystal display devices according to Examples 6and 7 of the present invention, and a liquid crystal display device asComparative Example 4 were fabricated as follows:

A mixture including a photopolymerizable material and a liquid crystalmaterial was prepared in each of Examples 6 and 7 and ComparativeExample 4. As the photopolymerizable material, 0.02 g oftrimethylolpropane triacrylate, 0.16 g of isobornyl acrylate, and 0.02 gof a fluorine-containing monomer consisting of β-(perfluorooctyl)ethylacrylate were used in each of Examples 6 and 7 and, Comparative Example4. As the liquid crystal material, 0.78 g of a fluorine-containingliquid crystal material (ZLI-4801-000, manufactured by Merck & Co.,Inc.), 0.78 g of a fluorine-chlorine-containing liquid crystal material(TL-202, manufactured by Merck & Co., Inc.), and 0.78 g of acyanobiphenyl-containing liquid crystal material (E-8, manufactured byMerck & Co., Inc.) were used, respectively, in Examples 6 and 7 andComparative Example 4. The liquid crystal display devices werefabricated using the above-mentioned mixtures, by the same method asthat in Example 1.

Similar measurements to those in Example 1 were taken with respect toeach liquid crystal display device; results of the measurements arelisted in Table 1. Electrooptical characteristics of each liquid crystaldevice at room temperature, after a liquid crystal cell thereof washeated at 80° C. for an hour, are listed in Table 2.

The liquid crystal devices of Examples 6 and 7 and Comparative Example 4include a polymer resin composition which contains a fluorine-containingpolymer and has a relatively high glass transition temperature T_(g).The liquid crystal devices of Examples 6 and 7, which use thefluorine-containing liquid crystal material, do not include a cyanogroup, a pyrimidine ring, or the like, which are likely to gatherimpurities. Therefore, the liquid crystal devices of Examples 6 and 7have a high voltage-holding ratio. Moreover, in Example 7, the liquidcrystal material used therein also contains chlorine, and therefore hasa large anisotropy Δn of refractive index, so that a light transmittanceT₀ thereof under no voltage applied is smaller than in the case ofExample 6. As a result, a contrast ratio T₁₀₀ /T₀ is greatly improved inExample 7.

The liquid crystal device of Comparative Example 4, on the other hand,uses the cyanobiphenyl-containing liquid crystal material. Therefore,the voltage-holding ratio of the liquid crystal cell thereof isinsufficient as compared with those of Examples 4, 5, 6, and 7,indicating that the liquid crystal device of Comparative Example 4 hassmall practicality.

Moreover, Examples 4, 6, and 7 are counterparts of, respectively,Examples 1, 2, and 3 with a difference that the fluorine-containingmonomer is added in Examples 4, 6, and 7; it was observed that avoltage-holding ratio HR of a liquid crystal cell of each of Examples 4,6, and 7 was slightly lower than those of the liquid crystal cells inExamples 1, 2, and 3, because of the addition of the fluorine-containingmonomer.

Comparative Example 5

As Comparative Example 2, a polymer dispersed liquid crystal displaydevice was fabricated as follows:

A homogeneous mixture containing 0.78 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.); and a photopolymerizablematerial consisting of 0.02 g of a bifunctional acrylate monomer (R-684,manufactured by Nippon Kayaku K.K.), 0.15 g of 2-ethylhexyl acrylate(Tg: -55° C.), and 0.03 g of a fluorine-containing monomer consisting ofβ-(perfluorooctyl)ethyl acrylate was prepared. The liquid crystaldisplay device was fabricated using the above-mentioned mixture, by thesame method as that in Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

Comparative Example 6

As Comparative Example 6, a polymer dispersed liquid crystal displaydevice was fabricated as follows:

A homogeneous mixture containing 0.78 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.); and a photopolymerizablematerial consisting of 0.02 g of trimethylol propane triacrylate, 0.05 gof n-lauryl acrylate (Tg: -30° C.), 0.10 g of 2-ethylhexyl acrylate, and0.03 g of a fluorine-containing monomer consisting ofβ-(perfluorooctyl)ethyl acrylate was prepared. The liquid crystaldisplay device was fabricated using the above-mentioned mixture, by thesame method as that in Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

The liquid crystal devices of Comparative Examples 5 and 6 include afluorine-containing polymer and use a monomer(s) having a low glasstransition temperature T_(g) as a main content of the polymerizablematerials thereof. Therefore, the liquid crystal devices of ComparativeExamples 5 and 6 have a large T value, indicative of insufficientelectrooptical characteristics and heat resistance. It can be seen thatthe liquid crystal devices of Examples 4, 5, 6, and 7 have improvedelectrooptical characteristics and heat resistance as compared withthose of the liquid crystal devices of Comparative Examples 5 and 6.

EXAMPLE 8

As Example 8 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing a liquid crystal material consisting of0.76 g of a fluorine-containing liquid crystal material (ZLI-4801-000,manufactured by Merck & Co., Inc.) and 0.01 g of a chiral dopant (S-811,manufactured by Merck & Co., Inc.); and a photopolymerizable materialconsisting of 0.02 g of trimethylolpropane triacrylate and 0.17 g ofisobornyl acrylate was prepared. The liquid crystal display device wasfabricated using the above-mentioned mixture, by the same method as thatin Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

EXAMPLE 9

As Example 9 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing a liquid crystal material consisting of0.76 g of a fluorine-containing liquid crystal material (ZLI-4801-000,manufactured by Merck & Co., Inc.) and 0.01 g of a chiral dopant (S-811,manufactured by Merck & Co., Inc.); and a polymerizable materialconsisting of 0.02 g of trimethylolpropane triacrylate, 0.15 g ofisobornyl acrylate, and 0.03 g of a fluorine-containing monomerconsisting of β-(perfluorooctyl)ethyl acrylate was prepared. The liquidcrystal display device was fabricated using the above-mentioned mixture,by the same method as that in Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

Furthermore, it can be seen that the response time τd is shortened inExamples 8 and 9, because the chiral dopants were added by a few percentto the liquid crystal materials used therein.

EXAMPLE 10

As Example 10 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing a dye-containing liquid crystalmaterial obtained by mixing 0.75 g of a fluorine-containing liquidcrystal material (ZLI-4801-000, manufactured by Merck & Co., Inc.) with0.03 g of an anthraquinone-type dichroic dye (D 37, manufactured by BDHLimited) having a maximal absorption wavelength at 556 nm; and aphotopolymerizable material consisting of 0.02 g of trimethylolpropanetriacrylate and 0.17 g of isobornyl acrylate was prepared. The liquidcrystal display device was fabricated using the above-mentioned mixture,by the same method as that in Example 1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

EXAMPLE 11

As Example 11 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing a dye-containing liquid crystalmaterial obtained by mixing 0.75 g of a fluorine-containing liquidcrystal material (ZLI-4801-000, manufactured by Merck & Co., Inc.) with0.03 g of an anthraquinone-type dichroic dye (D 37, manufactured by BDHLimited) having a maximal absorption wavelength at 556 nm; and apolymerizable material consisting of 0.02 g of trimethylolpropanetriacrylate, 0.15 g of isobornyl acrylate, and 0.03 g of afluorine-containing monomer consisting of β-(perfluorooctyl)ethylacrylate was prepared. The liquid crystal display device was fabricatedusing the above-mentioned mixture, by the same method as that in Example1.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

It was observed that the liquid crystal device of each of Examples 10and 11 was colored because of absorption of light in visible wavelengthsdue to the addition of the dichroic dye, whereby the contrast thereofwas slightly improved.

EXAMPLE 12

As Example 12 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

First, a homogeneous mixture containing 0.75 g of a fluorine-containingliquid crystal material (ZLI-4801-000, manufactured by Merck & Co.,Inc.); a polymerizable material for forming a polymer wall consisting of0.12 g of an aliphatic-type epoxy resin (thermosetting-resin DenacolEX-314, manufactured by Nagase Kasei Kogyo corporation); and a curingaccelerator consisting of 0.06 g of a modified-aliphatic-polyamine typecuring agent (Epomic Q-610, manufactured by Mitsui Petrochemical Co.,Ltd.) was prepared.

Next, a cell was formed using two glass plates (flint glass with ITOhaving a thickness of 500 Angstroms, manufactured by Nippon Sheet GlassCo., Ltd.) with spacers each having a diameter of 12 μm interposedtherebetween. Then, the above-mentioned mixture was injected into thecell. The cell was subjected to a heat treatment at 60° C. for an hour.Thus, phase separation of the liquid crystal composition and the polymercomposition was conducted through heat-polymerization so as to form aliquid crystal display device having a polymer dispersed liquid crystalcomplex film.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

EXAMPLE 13

As Example 13 of the present invention, a polymer dispersed liquidcrystal display device was fabricated as follows:

A homogeneous mixture containing 0.75 g of a fluorine-containing liquidcrystal material (ZLI-4801-000, manufactured by Merck & Co., Inc.); apolymerizable material for forming a polymer wall consisting of 0.12 gof an aliphatic-type epoxy resin (thermosetting-resin Denacol EX-314,manufactured by Nagase Kasei Kogyo corporation); a curing acceleratorconsisting of 0.06 g of a modified-aliphatic-polyamine type curing agent(Epomic Q-610, manufactured by Mitsui Petrochemical Co., Ltd.), and 0.02g of a silicon-containing monomer (KBM 403, manufactured by Shin-EtsuChemical Co., Ltd.) was prepared. The liquid crystal display device wasfabricated using the above-mentioned mixture, by the same method as thatin Example 12.

Similar measurements to those in Example 1 were taken with respect tothe liquid crystal display device; results of the measurements arelisted in Table 1.

                                      TABLE 1                                     __________________________________________________________________________           ΔT                                                                         Tg T.sub.0                                                                          T.sub.100                                                                        Vth                                                                              Vs τd                                                                           Δv/v.sub.50                                                                 HR (%)                                               (°C.)                                                                     (°C.)                                                                     (%)                                                                              (%)                                                                              (V)                                                                              (V)                                                                              (ms)                                                                             (%) (25° C.)                               __________________________________________________________________________    Example 1                                                                            8.0                                                                              74 9.2                                                                              77.6                                                                             6.2                                                                              8.0                                                                              40 5.8 98.1                                          Example 2                                                                            4.2                                                                              85 10.3                                                                             76.2                                                                             6.5                                                                              8.5                                                                              35 4.3 97.7                                          Example 3                                                                            3.8                                                                              85 1.0                                                                              80.4                                                                             4.3                                                                              6.2                                                                              20 3.5 98.0                                          Comparative                                                                          4.5                                                                              85 1.2                                                                              74.0                                                                             22.0                                                                             35.7                                                                             186                                                                              23.0                                                                              78.8                                          Example 1                                                                     Comparative                                                                          26.2                                                                             2.5                                                                              6.8                                                                              73.0                                                                             6.6                                                                              8.8                                                                              58 16.6                                                                              97.5                                          Example 2                                                                     Comparative                                                                          18.3                                                                             12 6.0                                                                              72.2                                                                             6.8                                                                              9.0                                                                              55 14.8                                                                              97.8                                          Example 3                                                                     Example 4                                                                            9.0                                                                              68 10.2                                                                             77.0                                                                             5.8                                                                              7.5                                                                              32 4.1 98.5                                          Example 5                                                                            8.6                                                                              71 9.0                                                                              75.1                                                                             5.5                                                                              7.5                                                                              35 4.8 89.8                                          Example 6                                                                            8.4                                                                              72 11.3                                                                             76.4                                                                             6.1                                                                              7.8                                                                              34 4.1 97.9                                          Example 7                                                                            8.2                                                                              72 1.1                                                                              75.0                                                                             5.4                                                                              7.3                                                                              18 3.0 98.4                                          Comparative                                                                          8.6                                                                              72 1.0                                                                              68.0                                                                             23.6                                                                             38.1                                                                             213                                                                              18.6                                                                              68.9                                          Example 4                                                                     Comparative                                                                          27.6                                                                             1.7                                                                              6.5                                                                              72.2                                                                             6.8                                                                              9.0                                                                              67 14.8                                                                              97.5                                          Example 5                                                                     Comparative                                                                          13.6                                                                             7.2                                                                              7.3                                                                              70.7                                                                             6.3                                                                              8.8                                                                              72 13.6                                                                              97.8                                          Example 6                                                                     Example 8                                                                            5.1                                                                              85 4.0                                                                              76.0                                                                             6.3                                                                              8.8                                                                              22 5.0 92.2                                          Example 9                                                                            8.0                                                                              75 3.8                                                                              75.1                                                                             8.7                                                                              11.0                                                                             17 4.3 89.7                                          Example 10                                                                           4.8                                                                              85 0.8                                                                              78.1                                                                             8.4                                                                              11.0                                                                             87 11.2                                                                              89.7                                          Example 11                                                                           8.2                                                                              75 0.9                                                                              76.2                                                                             10.5                                                                             12.7                                                                             82 10.3                                                                              87.3                                          Example 12                                                                           4.0                                                                              88 3.0                                                                              75.2                                                                             10.1                                                                             12.4                                                                             73 10.3                                                                              88.3                                          Example 13                                                                           7.2                                                                              81 4.3                                                                              75.3                                                                             10.1                                                                             12.3                                                                             67 9.8 89.5                                          __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                                 T.sub.0                                                                            T.sub.100                                                                             Contrast Ratio                                                                            Vth   Vs                                             (%)  (%)     T.sub.100 /T.sub.0                                                                        (V)   (V)                                   ______________________________________                                        Example 2  10.3   76.2    7.4       6.5   8.5                                 (Before Heating)                                                              Example 2  10.6   77.1    7.3       6.7   8.8                                 (Ater Heating)                                                                Example 3  1.0    80.4    80.4      4.3   6.2                                 (Before Heating)                                                              Example 3  1.1    81.0    73.6      4.6   6.3                                 (After Heating)                                                               Comparative                                                                              1.2    74.0    61.7      22.0  35.0                                Example 1                                                                     (Before Heating)                                                              Comparative                                                                              3.9    65.2    16.7      38.1  46.1                                Example 1                                                                     (After Heating)                                                               Example 6  11.3   76.4    6.8       6.1   7.8                                 (Before Heating)                                                              Example 6  11.6   77.5    6.7       6.5   8.3                                 (After Heating)                                                               Example 7  1.1    75.0    68.2      5.4   7.3                                 (Before Heating)                                                              Example 7  1.2    78.3    65.2      5.3   7.4                                 (After Heating)                                                               Comparative                                                                              1.0    68.0    68.0      23.6  38.1                                Example 4                                                                     (Before Heating)                                                              Comparative                                                                              3.8    64.2    16.9      37.1  46.6                                Example 4                                                                     (After Heating)                                                               ______________________________________                                    

EXAMPLE 14

As Example 14, a liquid crystal display device was fabricated asfollows:

First, a cell was formed using two glass plates (thickness: 1.1 mm),each glass plate having a transparent electrode made of ITO having athickness of 500 Angstroms formed thereon, with spacers each having adiameter of 6 μm interposed between the two glass plates so that thecell retained a certain thickness. Then, a photomask was disposed on thecell in such a way that pixel regions of the cell and masking portionsof the photomask corresponded to each other. FIG. 9 shows the photomaskused in the present example. As is shown in FIG. 9, the photomask hassquare masking portions 31 disposed in a matrix shape. One side of eachsquare masking portion 31 is 200 μm. Adjoining masking portions 31 arespaced by 50 μm. A light-transmitting hole 32 having a diameter of 25 μmis provided in the center of each masking portion 31.

Next, a mixture containing a photopolymerizable material consisting of0.1 g of a bifunctional acrylate monomer (R-684, manufactured by NipponKayaku K.K.), 0.05 g of p-phenylstyrene, 0.80 g of isobornylmethacrylate, and 0.05 g of perphlorooctyl acrylate; 4 g of a liquidcrystal material (ZLI-4792, manufactured by Merck & Co., Inc.) addedwith 0.3%, by weight, of a chiral dopant (S-811, manufactured by Merck &Co., Inc.); and 0.0025 g of a photopolymerization initiator (Irgacure651, manufactured by CIBA-GEIGY Corporation) was prepared. Theabove-mentioned mixture was observed while being heated, which revealedthat the mixture became homogeneous at 32° C. The mixture was heated to34° C. and was injected into the cell.

Twenty cycles of light-irradiation was conducted for the cell, intowhich the mixture had been injected; each cycle consisted of a stepwhere the cell was irradiated with parallel light beams through thephotomask while being kept at 34° C. (one second), and a step where nolight-irradiation was conducted (30 seconds). After the twenty cycles oflight-irradiation had been conducted, the cell was further irradiatedwith parallel light beams for 5 minutes. The parallel light beams wereobtained under a high-pressure mercury lamp where it had an illuminanceof 10 mW/cm². Then the temperature of the cell was lowered to 10° C.,and the cell was irradiated with UV-rays at the same illuminance of 10mW/cm² for 10 minutes while being kept at 10° C. Finally, the photomaskwas removed, and thereafter the cell was irradiated with UV-rays for 5minutes so that the polymerizable material cured.

FIG. 10 shows a plane view of the cell thus obtained, the cell beingobserved with a polarization microscope. As is shown in FIG. 10, aliquid crystal region 41 was surrounded by a polymer matrix 42, and aconfiguration thereof was substantially the same as that of each maskingportion 31 of the photomask. In the center of the liquid crystal region41, a polymer island 43 corresponding to each light-transmitting hole 32had been formed. Moreover, the liquid crystal region 41 was divided intoa plurality of liquid crystal domains 45 by disclination lines 44. Theliquid crystal domains 45 were arranged radially with the polymer island43 being a center.

Furthermore, a polarizing plate was attached to each of the upper sideand the back side of the cell in such a way that directions ofpolarization of the two polarizing plates were perpendicular to eachother, so as to form a polymer-matrix type liquid crystal displaydevice.

Table 3 shows electrooptical characteristics, a value ΔT, and the likeof this liquid crystal display device. As for light transmittances underno voltage applied, a light transmittance in the case where twopolarization plates disposed in a parallel-Nicol state is defined as100%. As for response times, they are evaluated using an addition(τd+τr), wherein τd represents a response time required for a lighttransmittance to vary by 90% after a voltage is stopped being applied,and τr represents a response time required for a light transmittance tovary by 90% after a voltage is started being applied.

FIG. 11 is a diagram showing the dependence of electroopticalcharacteristics of the liquid crystal display device on viewing angles,and consists of graphs (a) to (e). Graph (a) shows a relationshipbetween applied voltages and light transmittances in cases where, as isshown in FIG. 12, a direction a vertical to the liquid crystal displaydevice is the viewing angle. Graphs (b), (c), (d), and (e) showrelationships between applied voltages and light transmittances, andthey describe cases where the viewing angle is at an angle of 40° withrespect to the direction a so as to be tilted in, respectively,directions b, c, d, and e, as is shown in FIG. 12. As is seen from FIG.11, no such defects in viewing angle characteristics as an inversionphenomenon, where the contrast of a liquid crystal device is inverted,are found, irrespective of the viewing angle i.e. the direction in whichthe liquid crystal device is watched. The reason for this is that liquidcrystal molecules of the liquid crystal device stand in variousdirections when an outside voltage is applied because of an interactionthereof with the polymer matrix, whereby the same apparent refractiveindex is attained irrespective of the viewing angle.

Comparative Example 7

As Comparative Example 7, a liquid crystal display device was fabricatedas follows:

First, a cell was formed, with a similar mixture to that in Example 14injected therein. A similar photomask to that used in FIG. 14 wasdisposed on the cell.

Twenty cycles of light-irradiation were conducted for the cell; eachcycle consisted of a step where the cell was irradiated with parallellight beams through the photomask while being kept at 34° C. (onesecond), and a step where no light-irradiation was conducted (30seconds). After the twenty cycles of light-irradiation had beenconducted, the cell was further irradiated with parallel light beams for10 minutes. The parallel light beams were obtained under a high pressuremercury lamp where it had an illuminance of 10 mW/cm². The cell thusobtained was observed with a polarizing microscope, which revealed thatliquid crystal domains of the cell had substantially the sameorientation as that in Example 14.

Furthermore, a polarizing plate was attached to each of the upper sideand the back side of the cell in such a way that directions ofpolarization of the two polarizing plates were perpendicular to eachother, so as to form a polymer-matrix type liquid crystal displaydevice.

Table 3 shows electrooptical characteristics, a value ΔT, and the likeof this liquid crystal display device.

                  TABLE 3                                                         ______________________________________                                                   Example     Comparative                                                       14          Example 7                                              ______________________________________                                        light transmittance                                                                        38            38                                                 under no voltage                                                              applied (%)                                                                   response time                                                                              35            46                                                 τd + τr (ms)                                                          value ΔT (°C.)                                                                 2            5.6                                                T.sub.g of the polymer                                                                     in the vicinity of                                                                          in the vicinity of                                 (°C.) 75            75                                                 ______________________________________                                    

As is seen from Table 3, the liquid crystal display device of Example 14has a :small ΔT value, as compared with that of Comparative Example 7.In other words, impurities hardly dissolve into the liquid crystalmaterial in Example 14, whereby the response speed of the liquid crystaldevice is improved. Glass transition temperatures T_(g) of thephotopolymerizable materials alone were measured by a DSC method, whichrevealed that an absorption curve of photopolymerizable material had aninflection point in the vicinity of 75° C. Moreover, viewing anglecharacteristics of the liquid crystal display device of ComparativeExample 7 were also improved.

EXAMPLE 15

As Example 15, a liquid crystal display device was fabricated asfollows:

A mixture containing a photopolymerizable material consisting of 0.02 gof a bifunctional acrylate monomer (R-684, manufactured by Nippon KayakuK.K.), 0.14 g of isobornyl acrylate, and 0.02 g of p-phenylstyrene; 0.78g of a liquid crystal material (ZLI-4792, manufactured by Merck & Co.,Inc.); and 0.03 g of a photopolymerization initiator (Irgacure 651,manufactured by CIBA-GEIGY Corporation) was prepared. Theabove-mentioned mixture was observed while being heated, which revealedthat the mixture became homogeneous at 34° C. The mixture was heated to36° C. and was injected into a cell consisting of two glass substrateswith spacers each having a diameter of 12 μm interposed therebetween.The cell, into which the mixture had been injected, was irradiated withUV-rays for 60 seconds by means of a high-pressure mercury lamp at anilluminance of 50 mW/cm² so as to conduct a photopolymerization.

Then, the temperature of the cell was lowered to 5° C. at a rate of 1°C. per minute, and the cell was irradiated with UV-rays at anilluminance of 15 mW/cm² for 300 seconds, so as to sufficiently conducta phase separation, whereby a polymer dispersed liquid crystal displaydevice was fabricated. This liquid crystal display device was of a lightscattering-transmission mode.

In the present example, the phase separation at the second irradiationwith UV-rays is conducted in a temperature range where the mixture afterthe first irradiation with UV-rays has a liquid crystal phase at whichthe viscosity is higher than in an isotropic state and the liquidcrystal has a higher orientation property than at room temperature. Thisliquid crystal phase is, in the case of the present example, a smecticphase.

Table 4 shows electrooptical characteristics, a value ΔT, and the likeof this liquid crystal display device.

EXAMPLE 16

As Example 16, a liquid crystal display device was fabricated asfollows:

A mixture containing a photopolymerizable material consisting of 0.02 gof a bifunctional acrylate monomer (R-684, manufactured by Nippon KayakuK.K.), 0.14 g of isobornyl acrylate, and 0.02 g of p-phenylstyrene: 0.78g of a liquid crystal material (ZLI-4792, manufactured by Merck & Co.,Inc.); and a photopolymerization initiator consisting of 0.025 g ofIrgacure 651 (manufactured by CIBA-GEIGY Corporation) and 0.005 g ofbenzoylperoxide [BPO] was prepared. The above-mentioned mixture wasobserved while being heated, which revealed that the mixture becamehomogeneous at 34° C. The mixture was heated to 36° C. and was injectedinto a cell consisting of two glass substrates with spacers each havinga diameter of 12 μm interposed therebetween. The cell, into which themixture had been injected, was irradiated with UV-rays for 60 seconds bymeans of a high-pressure mercury lamp at an illuminance of 50 mW/cm², soas to conduct a photopolymerization.

Then, the temperature of the cell was lowered to 5° C. at a ratio of 1°C. per minute. Thereafter, while keeping a thermostatic chamber at 5° C.in which the cell was disposed, a surface of the cell was scanned with alaser beam having a diameter of 2 μm by means of a XeCl eximer laserhaving an output power of 100 mW/pulse, a pulse width of 1 nm, and awavelength of 308 nm, to form a polymer dispersed liquid crystal displaydevice. This liquid crystal display device was of a lightscattering-transmission mode.

In the present example, the first phase separation throughpolymerization is conducted by irradiation with UV-rays. Furthermore, asecond phase separation through polymerization is conducted by a heatingeffect due to the laser beam, in a temperature range where the mixtureafter the first irradiation with UV-rays has a liquid crystal phase atwhich the viscosity is higher than in an isotropic state and the liquidcrystal is more orderly than at room temperature.

Moreover, since the UV-ray XeCl eximer laser is used, the presentexample utilizes a synergistic effect of photoreaction by UV-rays aswell as the heating effect due to the laser beam; however, a heatingeffect by means of a solid-state laser such as a Nd:YAG laser, or a gaslaser such as an Ar-ion laser can generally be utilized alternatively.

Table 4 shows electrooptical characteristics, a value ΔT, and the likeof this liquid crystal display device.

                  TABLE 4                                                         ______________________________________                                                      Example 15                                                                            Example 16                                              ______________________________________                                        value ΔT (°C.)                                                                   5.1       5.8                                                 T.sub.g of the  76        76                                                  polymer (°C.)                                                          T.sub.0 (%)     1.2       1.5                                                 T.sub.100 (%)   77.8      76.9                                                τd + τr (ms)                                                                          40        43                                                  value ΔV/V.sub.50                                                                       4.2       4.5                                                 ______________________________________                                    

As is seen from Table 4, the liquid crystal display devices of Examples15 and 16 each include a polymer resin composition having a small ΔTvalue, whereby display characteristics such as voltage-transmittancehysteresis characteristics and response speeds thereof are improved. Thereason is that, in each of Examples 15 and 16, the second phaseseparation through polymerization is conducted at a low temperaturewhere the mixture has a liquid crystal state, so that mutual dissolutionof the liquid crystal composition and the polymer composition arerestrained, whereby liquid crystal regions and a polymer region of theliquid crystal device are more clearly distinguished because of thephase separation.

EXAMPLE 17

As Example 17, a liquid crystal display device was fabricated asfollows:

First, a cell was formed using two glass plates (thickness: 1.1 mm),each glass plate having a transparent electrode made of ITO having athickness 500 Angstroms formed thereon, with spacers each having adiameter of 6 μm interposed between the two glass plates so that thecell retained a certain thickness. Then, the photomask shown in FIG. 9was disposed on the cell in such a way that pixel regions of the celland masking portions of the photomask corresponded to each other.

Next, a mixture containing a photopolymerizable material consisting of0.1 g of a bifunctional acrylate monomer (R-684, manufactured by NipponKayaku K.K.), 0.05 g of p-phenylstyrene, and 0.85 g of isobornylmethacrylate; 4 g of a liquid crystal material (ZLI-4792, manufacturedby Merck & Co., Inc.) added with 0.3%, by weight, of a chiral dopant(S-811, manufactured by Merck & Co., Inc.); and 0.0025 g of aphotopolymerization initiator (Irgacure 651, manufactured by CIBA-GEIGYCorporation) was prepared. The above-mentioned mixture was observedwhile being heated, which revealed that the mixture became homogeneousat 32° C. The mixture was heated to 34° C. and was injected into thecell.

Twenty cycles of light-irradiation were conducted for the cell, intowhich the mixture had been injected; each cycle consisted of a stepwhere the cell was irradiated with parallel light beams through thephotomask while being kept at 34° C. (one second), and a step where nolight-irradiation was conducted (30 seconds). After the twenty cycles oflight-irradiation had been conducted, the cell was further irradiatedwith parallel light beams for 5 minutes. The parallel light beams wereobtained under a high-pressure mercury lamp where it had an illuminanceof 10 mW/cm². Then, the cell was irradiated with UV-rays at the sameilluminance of 10 mW/cm² for 10 minutes. Finally, the photomask wasremoved, and thereafter the cell was irradiated with UV-rays for 5minutes so that the polymerizable material cured.

The cell thus obtained was observed with a polarization microscope,which revealed that, as in Example 14, a pixel region (liquid crystalregion) had such a configuration that a plurality of liquid crystaldomains therein were oriented radially with a polymer island in thecenter.

Furthermore, a polarizing plate was attached to each of the upper sideand the back side of the cell in such a way that the directions ofpolarization of the two polarizing plates were perpendicular to eachother, so as to form a polymer-matrix type liquid crystal displaydevice.

Table 5 shows electrooptical characteristics, a value ΔT, and the likeof this liquid crystal display device. The electroopticalcharacteristics and thermal characteristics of the liquid crystal devicewere measured by means of a liquid crystal evaluating apparatus(LCD-5000, manufactured by OTSUKA ELECTRONICS CO., Ltd.). As for lighttransmittances, they were measured by measuring an outgoing beam fromthe liquid crystal display device when a light beam from a halogen lampwas incident to the liquid crystal display device at a right angle andan electric field was applied, the liquid crystal being in anormally-white state. A lens having a converging angle of 24° was used.A light transmittance in the case where two polarization plates disposedin a parallel-Nicol state is defined as 100%. As for contrast ratios,they are defined as a ratio T₀ /T_(sat), wherein T₀ is a lighttransmittance when a voltage is stopped being applied, and T_(sat) is alight transmittance under a saturation voltage is applied.

Comparative Example 8

As Comparative Example 8, a polymer-matrix type liquid crystal displaydevice was fabricated as follows:

A mixture containing a photopolymerizable material consisting of 0.20 gof a bifunctional acrylate monomer (R-684, manufactured by Nippon KayakuK.K.), 0.02 g of p-phenylstyrene, 0.50 g of 2-ethylhexyl methacrylate,and 0.25 g of lauryl methacrylate; 4 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.) added with 0.3%, byweight, of a chiral dopant (S-811, manufactured by Merck & Co., Inc.);and 0.0025 g of a photopolymerization initiator (Irgacure 651,manufactured by CIBA-GEIGY Corporation) was prepared. Theabove-mentioned mixture was observed while being heated, which revealedthat the mixture became homogeneous at 26° C. The mixture was heated to29° C. and was injected into a cell formed in the same manner as that inExample 17. Thereafter, a liquid crystal cell was formed while keepingthe cell at 29° C., in the same manner as that in Example 17.Furthermore, a polarizing plate was attached to each of the upper sideand the back side of the cell in such a way that directions ofpolarization of the two polarizing plates were perpendicular to eachother, so as to form a polymer-matrix type liquid crystal displaydevice.

Table 5 shows electrooptical characteristics, a value ΔT, and the likeof this liquid crystal display device.

                  TABLE 5                                                         ______________________________________                                                      Example                                                                              Comparative                                                            17     Example 8                                                ______________________________________                                        value ΔT (°C.)                                                                   4.8      26.1                                                 T.sub.g of the  77       4                                                    polymer (°C.)                                                          V.sub.th (V)    2.5      4.1                                                  τd + τr (ms)                                                                          35       83                                                   contrast ratio  38       31                                                   ______________________________________                                    

As is seen from Table 5, the liquid crystal display device of Example 17has a small ΔT value, and the photopolymerizable material has a highT_(g). Therefore, mutual dissolution of the liquid crystal compositionand the polymer resin composition are restrained, whereby thresholdcharacteristics of voltage-transmittance characteristics and a responsespeed (τd+τr) of the liquid crystal device are improved.

Moreover, by using a photomask, the liquid crystal regions were clearlydistinguished. As a result, the same apparent refractive index wasattained irrespective of the viewing angle, whereby viewingcharacteristics of the liquid crystal device were improved. No suchdefects in viewing angle characteristics as an inversion phenomenon,i.e. inversion of contrast of the liquid crystal device, were found atany viewing angle. Moreover, change in contrast due to change in theviewing angle was small.

As is described above, a polymer dispersed liquid crystal complex filmand a liquid crystal display device according to Examples 1 to 17 of thepresent invention, since a polymer wall (matrix) having a small ΔT valueand a high glass transition temperature T_(g) is introduced therein, canhave display characteristics which are not affected by changes inthermal circumstances. Moreover, it is made possible to provide apolymer dispersed liquid crystal display device and a polymer-matrixtype liquid crystal display device capable of responding at a higherspeed than conventionally, displaying tones of different levels, andoperating with a small voltage-transmittance hysteresis. Apolymer-matrix type liquid crystal display device according to thepresent invention has highly stable display characteristics andexcellent viewing characteristics.

EXAMPLE 18

FIGS. 13A to 13C are cross-sectional views showing a liquid crystal cell51 of a TN type according to Example 18. The liquid crystal cell 51 of aTN type included, a pair of glass substrates 52 and 53 (thickness: 1.1mm), a plurality of pixel electrodes 55 formed in a matrix shape on thesubstrate 52, a common electrode 56 formed on the other substrate 53,liquid crystal regions 54 interposed between the substrates 52 and 53,and a polymer matrix 57. Each liquid crystal region 54 corresponded toand covered each pixel electrode 55. A pixel region 58 corresponded to aregion of the liquid crystal cell 51 where each pixel electrode 55 wasformed. Hereinafter, a method for fabricating the liquid crystal cell 51of the present example will be described.

The pixel electrodes 55 and the common electrode 56 were transparent,and were made of ITO having a thickness 500 Angstroms. The transparentpixel electrodes 55 and the glass substrate 52 are, as a whole, definedas a display substrate 60. The transparent common electrode 56 and theglass substrate 53 are, as a whole, defined as a display substrate 61.Then, a cell was formed using the display substrates 60 and 61, withspacers (not shown) each having a diameter of 6 μm interposedtherebetween so that the cell retained a certain thickness. The spacershad a spherical shape in the present example, however, they mayalternatively have a cylindrical shape or a fiber-like shape. Thedisplay substrates 60 and 61 were sealed with a sealing material atperipheral portions thereof. Then, the photomask shown in FIG. 9 wasdisposed on the cell in such a way that pixel regions of the cell andmasking portions of the photomask corresponded to each other.

Next, a mixture containing 4 g of a liquid crystal material (ZLI-4792,manufactured by Merck & Co., Inc.) added with 0.3%, by weight, of achiral dopant (S-S11, manufactured by Merck & Co., Inc.); aphotopolymerizable material consisting of 0.1 g of a bifunctionalacrylate monomer (R-684, manufactured by Nippon Kayaku K.K.), 0.05 g ofp-phenylstyrene, and 0.85 g of isobornyl methacrylate; and 0.0025 g of aphotopolymerization initiator (Irgacure 651, manufactured by CIBA-GEIGYCorporation) was prepared. The above-mentioned mixture was observedwhile being heated, which revealed that the mixture became homogeneousat 32° C.

The liquid crystal regions 54 and the polymer matrix 57 were formed inthe following manner: First, the above-mentioned mixture was heated to34° C. and was injected into the cell. Then, twenty cycles oflight-irradiation were conducted for the cell, each cycle consisting ofa step where the cell was irradiated with parallel light beams throughthe photomask while being kept at 34° C. (one second), and a step whereno light-irradiation was conducted (30 seconds). The parallel lightbeams were obtained under a high-pressure mercury lamp where it had anilluminance of 10 mW/cm². After the twenty cycles of light-irradiationhad been conducted, the cell was further irradiated with parallel lightbeams for 5 minutes. Then, the cell was irradiated with UV-rays at thesame illuminance of 10 mW/cm² for 10 minutes. Finally, the photomask wasremoved, and thereafter the cell was irradiated with UV-rays for 5minutes so that the polymerizable material in the mixture curedcompletely.

The liquid crystal regions 54 and the polymer matrix 57 interposedbetween the pair of display substrates 60 and 61 were obtained throughthe above-mentioned polymerization process. FIG. 14 shows a plane viewof the liquid crystal cell 51 thus obtained, the liquid crystal cell 51being observed with a polarization microscope. As is shown in FIG. 14,each liquid crystal region 51 (corresponding to each pixel region 58)was divided into a plurality of liquid crystal domains 62 bydisclination lines 63. The disclination lines started from anisland-like portion formed in the center of each pixel region 58. Thedisclination lines 63 were formed radially or randomly, and they formedinterfaces between one liquid crystal domain 62 and another. The liquidcrystal domains 63, accordingly, were arranged radially or randomly withthe island-like portion being a center.

Furthermore, a polarizing plate was attached to each of the upper sideand the back side of the cell in such a way that directions ofpolarization of the two polarizing plates were perpendicular to eachother, so as to form a polymer-matrix type liquid crystal displaydevice.

Electrooptical characteristics (such as light transmittances, contrastratios, etc.) and thermal characteristics of the liquid crystal displaydevice were measured by means of a liquid crystal evaluating apparatus(LCD-5000, manufactured by OTSUKA ELECTRONICS CO., Ltd.) in thefollowing manner: A light transmittance in the case where twopolarization plates disposed in a parallel-Nicol state was defined as100%. The measurements for the liquid crystal display device wereconducted in a normally-white state. A light beam from a halogen lampwas incident to the liquid crystal display device at a right angle withrespect to the substrates 52 and 53. Then, as is shown in FIGS. 13A and13C, an electric field was turned on/off by applying/not applying avoltage to the liquid crystal display device by means of a power supply64, while the above-mentioned light beam was incident to the liquidcrystal display device. The light transmittances were measured bymeasuring four outgoing beams of the liquid crystal display device withlenses having a converging angle of 24°. All of the measured outgoingbeams constituted an angle of 40° with respect to a vertical axis of thesubstrate 52. However, one measured outgoing beam tilted toward the topof the substrate 52 in a longitudinal direction; another measuredoutgoing beam tilted toward the bottom of the substrate 52 in thelongitudinal direction; still another measured outgoing beam tilted tothe right in a latitudinal direction; the other measured outgoing beamtilted to the left in the latitudinal direction. A ratio T_(OFF) /T_(ON)was measured with respect to each of the four measured outgoing beams,wherein T_(OFF) is a light transmittance when no voltage is applied, andT_(ON) is a light transmittance when a voltage is applied. The contrastratios CR were defined as a mean of the four resultant ratios T_(OFF)/T_(ON).

Next, for the purpose of measuring the refractive index of the polymermatrix 57, a polymer resin film was fabricated in the following manner:First, a homogeneous mixture containing 0.3 g of the above-mentionedphotopolymerizable material and 0.0015 g of the above-mentionedphotopolymerization initiator was also prepared. The mixture wasinjected into a cell consisting essentially of glass substrates(thickness: 6 μm). The cell was then irradiated with UV-rays for 3minutes, whereby the photopolymerizable material was cured so as to forma polymer resin film. The UV-rays were obtained under a high-pressuremercury lamp where it had an illuminance of 10 mW/cm². The polymer resinfilm thus cured was taken out of the cell. Then, a refractive index ofthe polymer resin film was measured by means of an Abbe's refractometerat room temperature (25° C.). Results of the above-mentionedmeasurements are listed in Table 6.

In the present Example, phase separation of the liquid crystal and thepolymer is controlled with the photomask so that the liquid crystal andthe polymer are formed with regularity. Therefore, the liquid crystaldomains 62 within each liquid crystal region 54 are oriented radially orrandomly, as is described above. As a result, liquid crystal molecules65 as a whole stand omnidirectionally, whereby viewing anglecharacteristics of the liquid crystal display device of the presentexample are improved.

A main objective of the present invention is to improve the contrast ofthe liquid crystal display device and especially to minimize thecoarseness problem of a displayed image by restraining the scattering oflight occurring due to a difference in the refractive indices of eachliquid crystal region 54 and the polymer matrix 57. In the presentexample, the difference in the refractive indices of each liquid crystalregion 54 and the polymer matrix 57 is kept small by ensuring that arefractive index n_(p) of the polymer matrix 57 falls within a rangebetween [an ordinary refractive index n_(o) of each liquid crystalmolecule 65-0.04] and the refractive index (n_(e) +n_(o))/2 of eachliquid crystal molecule 65 in a randomly oriented state.

Herein, the following hold with reference to FIG. 15:

(A) When the refractive index n_(p) of the polymer matrix 57 is smallerthan [the ordinary refractive index n_(O) of each liquid crystalmolecule 65-0.04], the refractive index n_(p) and the refractive index(n_(e) +n_(o))/2 of the liquid crystal molecule 65 in a randomlyoriented state have a large difference. Therefore, the coarsenessproblem under no voltage applied worsens.

(B) When the refractive index n_(p) of the polymer matrix 57 is largerthan the refractive index (n_(e) +n_(o))/2 of each liquid crystalmolecule 65 in a randomly oriented state, the refractive index n_(p) andthe ordinary refractive index n_(o) of the liquid crystal molecule 65have a large difference. Therefore, the coarseness problem under avoltage applied worsens.

(C) By ensuring that the refractive index n_(p) of the polymer matrix 57is in a range between [the ordinary refractive index n_(o) of eachliquid crystal molecule 65-0.04] and the refractive index (n_(e)+n_(o))/2 of the liquid crystal molecule 65 in a randomly orientedstate, the difference between the refractive index of the liquid crystalmolecule 65 and the refractive index n_(p) of the polymer matrix 57 canbe made small in both of i) cases where a voltage is applied to theliquid crystal cell 51 (that is to say, the difference between theordinary refractive index n_(o) of the liquid crystal molecule 65 andthe refractive index n_(p) of the polymer matrix 57 is small) and ii)cases where no voltage is applied to the liquid crystal cell 51 (that isto say, the difference between the refractive index (n_(e) +n_(o))/2 ofthe liquid crystal molecule 65 in a randomly oriented state and therefractive index n_(p) of the polymer matrix 57 is small).

Moreover, the difference between the refractive index of the liquidcrystal molecule 65 and that of the polymer matrix 57 can be made tovary within only a small range in spite of changes in voltage between astate where a voltage is applied and a state where no voltage isapplied.

Thus, the contrast of the liquid crystal display device is improved, andthe coarseness problem of a displayed image can be minimized.

EXAMPLE 19

As Example 19, a liquid crystal display device and a polymer resin filmwere fabricated as follows:

A homogeneous mixture containing 4 g of a liquid crystal material(ZLI-5080, manufactured by Merck & Co., Inc.) added with 0.3%, byweight, of a chiral dopant (S-811, manufactured by Merck & Co., Inc.); aphotopolymerizable material consisting of 0.1 g of n-butylmethacrylate,0.85 g of perfluorooctyl methacrylate, and 0.05 g of styrene; and 0.0025g of a photopolymerization initiator (Irgacure 651, manufactured byCIBA-GEIGY Corporation) was prepared. For the purpose of measuringrefractive indices, a homogeneous mixture containing the above-mentionedphotopolymerizable material and photopolymerization initiator was alsoprepared. Thereafter, the liquid crystal display device and the polymerresin film were fabricated in the same manner as in Example 18,respectively using the above-mentioned mixtures. Then, variousrefractive indices of the liquid crystal display device and the polymerresin film were measured. Results of the measurements are listed belowin Table 6.

Comparative Example 9

As Comparative Example 9, a liquid crystal display device and a polymerresin film were fabricated as follows:

A homogeneous mixture containing 4 g of a liquid crystal material(ZLI-5048-000, manufactured by Merck & Co., Inc.) added with 0.3%, byweight, of a chiral dopant (S-811, manufactured by Merck & Co., Inc.); aphotopolymerizable material consisting of 0.95 g of a bifunctionalacrylate monomer (R-604, manufactured by Nippon Kayaku K.K.) and 0.05 gof styrene; and 0.0025 g of a photopolymerization initiator (Irgacure651, manufactured by CIBA-GEIGY Corporation) was prepared. For thepurpose of measuring refractive indices, a homogeneous mixturecontaining the above-mentioned photopolymerizable material andphotopolymerization initiator was also prepared. Thereafter, the liquidcrystal display device and the polymer resin film were fabricated in thesame manner as in Example 18, respectively using the above-mentionedmixtures. Then, various refractive indices of the liquid crystal displaydevice and the polymer resin film were measured. Results of themeasurements are listed below in Table 6.

Comparative Example 10

As Comparative Example 10, a liquid crystal display device and a polymerresin film were fabricated as follows:

A homogeneous mixture containing 4 g of a liquid crystal material(ZLI-4281, manufactured by Merck & Co., Inc.) added with 0.3%, byweight, of a chiral dopant (S-811, manufactured by Merck & Co., Inc.), aphotopolymerizable material consisting of 0.95 g of a bifunctionalacrylate monomer (R-684, manufactured by Nippon Kayaku K.K.) and 0.05 gof styrene, and 0.0025 g of a photopolymerization initiator (Irgacure651, manufactured by CIBA-GEIGY Corporation) was prepared. For thepurpose of measuring refractive indices, a homogeneous mixturecontaining the above-mentioned photopolymerizable material andphotopolymerization initiator was also prepared. Thereafter, the liquidcrystal display device and the polymer resin film were fabricated in thesame manner as in Example 18, respectively using the above-mentionedmixtures. Then, various refractive indices of the liquid crystal displaydevice and the polymer resin film were measured. Results of themeasurements are listed below in Table 6.

Comparative Example 11

As Comparative Example 11, a liquid crystal display device and a polymerresin film were fabricated as follows:

A homogeneous mixture containing 4 g of a liquid crystal material(ZLI-4792, manufactured by Merck & Co., Inc.) added with 0.3%, byweight, of a chiral dopant (S-811, manufactured by Merck & Co., Inc.); aphotopolymerizable material consisting of 0.95 g of a bifunctionalacrylate monomer (R-684, manufactured by Nippon Kayaku K.K.) and 0.05 gof styrene; and 0.0025 g of a photopolymerization initiator (Irgacure651, manufactured by CIBA-GEIGY Corporation) was prepared. For thepurpose of measuring refractive indices, a homogeneous mixturecontaining the above-mentioned photopolymerizable material andphotopolymerization initiator was also prepared. Thereafter, the liquidcrystal display device and the polymer resin film were fabricated in thesame manner as in Example 18, respectively using the above-mentionedmixtures. Then, various refractive indices of the liquid crystal displaydevice and the polymer resin film were measured. Results of themeasurements are listed below in Table 6.

                  TABLE 6                                                         ______________________________________                                                                              contrast                                       n.sub.p                                                                            n.sub.o                                                                              (n.sub.e + n.sub.o)/2                                                                    |n.sub.o - n.sub.p |                                                ratio CR                                ______________________________________                                        Example 18                                                                             1.500  1.479  1.526    0.021   41                                    Example 19                                                                             1.485  1.471  1.513    0.014   47                                    Comparative                                                                            1.450  1.504  1.574    0.054   28                                    Example 9                                                                     Comparative                                                                            1.535  1.474  1.496    0.061   18                                    Example 10                                                                    Comparative                                                                            1.535  1.479  1.526    0.056   25                                    Example 11                                                                    ______________________________________                                    

In each of Examples 18 and 19, as is seen from Table 6, it is ensuredthat a refractive index n_(p) of the polymer matrix falls within a rangebetween [an ordinary refractive index n_(o) of each liquid crystalmolecule-0.04] and the refractive index (n_(e) +n_(o)) /2 of each liquidcrystal molecule in a randomly oriented state, as was prescribedearlier. A difference in the refractive indices of each liquid crystalregion and the polymer matrix is therefore reduced, whereby scatteringof light at interfaces of the liquid crystal regions and the polymermatrix is minimized. As a result, the coarseness problem of a displayedimage is alleviated. It can be seen that the liquid crystal displaydevices of Examples 18 and 19 have higher contrast ratios than those ofthe liquid crystal display devices of Comparative Examples 9 and 10,whose refractive indices n_(o), n_(p), and n_(e) do not meet theabove-mentioned relationship.

Moreover, it is observed that the liquid crystal display device ofComparative Example 11 has a very low contrast ratio as compared to thatof the liquid crystal display device of Example 18, although the sameliquid crystal material is used in Example 18 and Comparative Example11. This is because, in Comparative Example 11, a refractive index n_(p)of the polymer matrix, an ordinary refractive index n_(o) of each liquidcrystal molecule, and an extraordinary refractive index n_(e) of eachliquid crystal molecule do not meet the above-mentioned relationship.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A method for producing a liquid crystal displaydevice including the steps of:preparing a mixture of a polymerizablematerial and a liquid crystal material; and forming a display mediummade of a polymer resin composition and a liquid crystal composition byphase separation through polymerization conducted by irradiating themixture with light having a distribution of intensities ranging fromhigh to low, the display medium interposed between a pair of substrates;and forming the polymer resin composition with a refractive index n_(p)and the liquid crystal composition with an ordinary refractive indexn_(o) and an extraordinary refractive index n_(e) in such a way so as tosatisfy the following relationship:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2.


2. A method for producing a liquid crystal display according to claim 1,wherein the light having a distribution of intensities ranging from highto low is obtained by substantially lowering the intensity of the lightat a pixel region.
 3. A method for producing a liquid crystal displayaccording to claim 1, wherein the display medium forming step includes afirst phase separation step for phase-separating the mixture throughpolymerization, and a second phase separation step for furtherphase-separating the mixture through polymerization, the second phaseseparation step being conducted at a lower temperature than the firstphase separation step.
 4. A method for producing a liquid crystaldisplay device including the steps of:preparing a mixture of apolymerizable material including at least one of a fluorine-containingpolymer, a chlorine-containing polymer, and a silicone-containingpolymer and a liquid crystal material including at least one of afluorine-containing compound and a chlorine-containing compound; forminga display medium made of a polymer resin composition and a liquidcrystal composition by phase separation through polymerization conductedby irradiating the mixture with light having a distribution ofintensities ranging from high to low, the display medium interposedbetween a pair of substrates; and forming the polymer resin compositionwith a refractive index n_(p) and the liquid crystal composition with anordinary refractive index n_(o) and an extraordinary refractive indexn_(e) in such a way so as to satisfy the following relationship:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2.


5. A method for producing a liquid crystal display according to claim 4,wherein the light having a distribution of intensities ranging from highto low is obtained by substantially lowering the intensity of the lightat a pixel region.
 6. A method for producing a liquid crystal displaydevice according to claim 4, wherein the liquid crystal compositionfurther includes one dichroic dye.
 7. A method for producing a liquidcrystal display device according to claim 4, wherein the liquid crystalcomposition further includes at least one of an optically active chiraldopant and a cholesteric liquid crystal added in a ratio, by weight, inthe range of 0.1% to 10% thereto.
 8. A method for producing a liquidcrystal display according to claim 4, wherein the display medium formingstep includes a first phase separation step for phase-separating themixture through polymerization, and a second phase separation step forfurther phase-separating the mixture through polymerization, the secondphase separation step being conducted at a lower temperature than thefirst phase separation step.
 9. A method for producing a liquid crystaldisplay device including the steps of:preparing a mixture of apolymerizable material and a liquid crystal material; forming a displaymedium made of a polymer resin composition and a liquid crystalcomposition of phase separation through polymerization conducted byirradiating the mixture with light having a distribution of intensitiesranging from high to low thereby forming a plurality of pixelspartitioned by a polymer matrix, each pixel comprising at least oneliquid crystal region, the display medium interposed between a pair ofsubstrates; and forming the polymer resin composition with a refractiveindex n_(p) and the liquid crystal composition with an ordinaryrefractive index n_(o) and an extraordinary refractive index n_(e) insuch a way so as to satisfy the following relationship:

    n.sub.o -0.04≦n.sub.p ≦(n.sub.e +n.sub.o)/2.


10. A method for producing a liquid crystal display according to claim9, wherein the light having a distribution of intensities ranging fromhigh to low is obtained by substantially lowering the intensity of thelight at a pixel region.
 11. A method for producing a liquid crystaldisplay device according to claim 9, wherein the liquid crystalcomposition further includes one dichroic dye.
 12. A method forproducing a liquid crystal display device according to claim 9, whereinthe liquid crystal composition further includes at least one of anoptically active chiral dopant and a cholesteric liquid crystal added ina ratio, by weight, in the range of 0.1% to 10% thereto.
 13. A methodfor producing a liquid crystal display according to claim 9, wherein thedisplay medium forming step includes a first phase separation step forphase-separating the mixture through polymerization, and a second phaseseparation step for further phase-separating the mixture throughpolymerization, the second phase separation step being conducted at alower temperature than the first phase separation step.